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C o 


u .r> 



United States Region III Region III EPA 903-R-03-002 

Environmental Protection Chesapeake Bay Water Protection October 2004 

Agency Program Office Division 

In coordination with the Office of Water/Office of Science and Technology, Washington, DC 


Ambient Water Quality 
Criteria for Dissolved 
Oxygen, Water Clarity and 
Chlorophyll a for the 
Chesapeake Bay and Its 
Tidal Tributaries 


f \ \ c • 


2004 Addendum 


October 2004 


A 




A 










K ft* 

V 







Ambient Water Quality Criteria 

M 

for Dissolved Oxygen, Water Clarity 
and Chlorophyll a for the Chesapeake Bay 

and Its Tidal Tributaries 


2004 Addendum 


October 2004 

U.S. Environmental Protection Agency 
Region III 

Chesapeake Bay Program Office 
Annapolis, Maryland 

and 

Region III 

Water Protection Division 
Philadelphia, Pennsylvania 

in coordination with 

Office of Water 

Office of Science and Technology 
Washington, D.C. 


72 ) 

,^ 3 /h/73 

* 7 } 1 


LC Control Number 


2006 530195 



































Ill 


Contents 

Acknowledgments . v 

I. Introduction . 1 

II. Shortnose Sturgeon Temperature Sensitivity Analyses . 3 

III. Key Findings Published in the EPA ESA 

Shortnose Sturgeon Biological Evaluation . 9 

Consultation History . 9 

Biological Evaluation Findings. 11 

Biological Evaluation Conclusions. 13 

Literature Cited . 15 

IV. Key Findings Published in the NOAA ESA 

Shortnose Sturgeon Biological Opinion . 17 

Chlorophyll a Criteria. 17 

Water Clarity Criteria. 17 

Dissolved Oxygen Criteria. 18 

Sea turtles. 18 

Shortnose sturgeon. 18 

Incidental Take Statement. 20 

Amount and Extent of Take Anticipated. 20 

Extent of take from 2004-2009 . 22 

Extent of take in 2010 and beyond . 23 

Reasonable and Prudent Measures . 23 

Literature Cited . 24 

V. Guidance for Attainment Assessment of Instantaneous 

Minimum and 7-Day Mean Dissolved Oxygen Criteria . 27 

Background. 27 

Current Status . 27 

Assessment of Instantaneous Minimum Criteria 

Attainment from Monthly Mean Data. 28 

Reference points with respect to depth. 29 

Data assemblage and manipulation. 29 

Designated use assignments . 36 

Findings. 36 


Contents 






























IV 


Assessment of 7-Day Mean Criteria Attainment 


from Monthly Mean Data Findings. 64 

Findings . 66 

Literature Cited . 66 


VI. Guidance for Deriving Site Specific Dissolved Oxygen Criteria 
for and Assessing Criteria Attainment of Naturally Low 
Dissolved Oxygen Concentrations in Tidal Wetland 


Influenced Estuarine Systems . 67 

Natural Conditions/Features Indicating Role of 

Wetlands in Low Dissolved Oxygen Concentrations . 68 

Surface to volume ratios/large fringing wetland areas . 68 

Water quality conditions . 68 

Dissolved oxygen/temperature relationships . \. 71 

Low variability in dissolved oxygen concentrations. 71 

Approaches for Addressing Naturally Low Dissolved Oxygen 

Conditions Due to Tidal Wetlands . 73 

Derivation of Site-Specific Dissolved Oxygen Criteria Factoring 
in Natural Wetland-Caused Dissolved Oxygen Deficits . 76 

Scientific research-based estimates of wetland respiration .... 77 

Model-based wetland-caused oxygen deficits. 77 

Monitoring-based estimates of wetland-caused oxygen deficits 78 

Site-specific dissolved oxygen criteria derivation. 81 

Site-specific criteria biological reference curve . 82 

Literature Cited . 83 

VII. Upper and Lower Pycnocline Boundary Delineation 

Methodology . 85 

Determination of the Vertical Density Profile . 86 

Determination of the Pycnocline Depths. 86 

Literature Cited . 87 

VIII. Updated Guidance for Application of Water Clarity Criteria 

and SAV Restoration Goal Acreages . 89 

Water Clarity Criteria Application Periods . 90 

Shallow-w ater Habitat Acreages. 91 

SAV restoration acreage to shallow-water habitat acreage ratio 91 

SAV Restoration Goal Acreages. 92 

Determining Attainment of the Shallow-w ater Bay Grass Use . . 93 
Literature Cited . 94 

IX. Determining Where Numerical Chlorophyll a Criteria 
Should Apply to Local Chesapeake Bay and 

Tidal Tributary Waters . 87 

Recommended Methodology . 97 

Literature Cited . 99 

Appendix A: Wetland Area, Segment Perimenter/Area/Volume 

and Water Quality Parameter Statistics for Chesapeake Bay 

Tidal Fresh and Oligohaline Segments . 101 


Contents 






























V 


Acknowledgments 


This addendum to the April 2003 Water Quality Criteria for Dissolved Oxygen, 
Water Clarity • and Chlorophyll a for Chesapeake Bay and Its Tidal Tributaries was 
developed and documented through the collaborative efforts of the members of the 
Chesapeake Bay Program's Water Quality Standards Coordinators Team: Richard 
Batiuk, U.S. EPA Region III Chesapeake Bay Program Office; Joe Beaman, Mary¬ 
land Department of the Environment; Gregory Hope, District of Columbia 
Department of Health; Libby Chatfield, West Virginia Environmental Quality Board; 
Tiffany Crawford, U.S. EPA Region III Water Protection Division; Elleanore Daub, 
Virginia Department of Environmental Quality; Lisa Huff, U.S. EPA Office of 
Water; Wayne Jackson, U.S. EPA Region II; James Keating, U.S. EPA Office of 
Water; Robert Koroncai, U.S. EPA Region III Water Protection Division; Benita 
Moore, Pennsylvania Department of Environmental Protection; Shah Nawaz, 
District of Columbia Department of Health; Scott Stoner, New York State Depart¬ 
ment of Environmental Conservation; David Wolanski, Delaware Department of 
Natural Resources and Environmental Control; and Carol Young, Pennsylvania 
Department of Environmental Protection. 

The individual and collective contributions from members of the Chesapeake Bay 
Program Office and NOAA Chesapeake Bay Office staff are also acknowledged: 
Danielle Algazi, U.S. EPA Region III Chesapeake Bay Program Office; David 
Jasinski, University of Maryland Center for Environmental Science/Chesapeake Bay 
Program Office; Marcia Olson, NOAA Chesapeake Bay Office; Gary Shenk, U.S. 
EPA Region III Chesapeake Bay Program Office; and Howard Weinberg, University 
of Maryland Center for Environmental Science/Chesapeake Bay Program Office. 


Acknowledgments 




1 


chapter | 


Introduction 


In April 2003, the U.S. Environmental Protection Agency (EPA) published the 
Ambient Water Quality> Criteria for Dissolved Oxygen, Water Clarity and Chloro¬ 
phyll a for the Chesapeake Bay and Its Tidal Tributaries (Regional Criteria 
Guidance) in cooperation with and on behalf of the six watershed states—New York, 
Pennsylvania, Maryland, Delaware, Virginia and West Virginia—and the District of 
Columbia. The culmination of three years of work, the Regional Criteria Guidance 
document was the direct result of the collective contributions of hundreds of regional 
scientists, technical staff and agency managers and the independent review by recog¬ 
nized experts across the country. 

At the time of publication of the Regional Criteria Guidance document, a number of 
technical issues still remained to be worked through, resolved and documented. The 
Chesapeake Bay Water Quality Standards Coordinators Team—water quality stan¬ 
dards program managers and coordinators from the seven Chesapeake Bay 
watershed jurisdictions and EPA’s Office of Water, Region 2 and Region 3—took on 
the responsibility on behalf of the Chesapeake Bay watershed partners to collectively 
work through these technical issues. The work on these issues was largely in support 
of the four jurisdictions with bay tidal waters who were formally adopting the 
published Chesapeake Bay water quality criteria, designated uses and criteria attain¬ 
ment procedures into their states’ water quality standards regulations. 

This first EPA published addendum to the 2003 Ambient Water Quality Criteria for 
Dissolved Oxygen, Water Clarity and Chlorophyll a for the Chesapeake Bay and Its 
Tidal Tributaries documents the resolution of and recommendations for addressing 
the following technical issues and criteria attainment procedures. 

• Guidance to the jurisdictions on where and when to apply the temperature-based 
open-water 4.3 mg liter 1 instantaneous minimum dissolved oxygen criteria 
required to protect the endangered shortnose sturgeon (Chapter 2). 

• Key findings published in the Endangered Species Act required EPA shortnose 
sturgeon biological evaluation of the potential impacts and benefits from publica¬ 
tion of the Regional Criteria Guidance (Chapter 3). 


chapter i 


Introduction 



2 


• Summary of findings, incidental take and recommended reasonable and prudent 
measures published in the Endangered Species Act required NOAA shortnose 
sturgeon biological opinion on the potential impacts and benefits from state adop¬ 
tion of the Regional Criteria Guidance into water quality standards (Chapter 4). 

• Guidance to the jurisdictions on when and where attainment of the instantaneous 
minimum, 1-day mean and 7-day mean dissolved oxygen criteria can be assessed 
using monthly mean water quality monitoring data (Chapter 5). 

• Guidance to the jurisdictions for deriving site-specific dissolved oxygen criteria 
and assessing criteria attainment of those tidal systems where naturally low 
dissolved oxygen concentrations are due to extensive adjacent tidal wetlands 
(Chapter 6). 

• Documentation of the methodology for delineating the upper and lower bound¬ 
aries of the pycnocline used in defining the vertical boundaries between 
open-water, deep-water and deep-channel designated uses (Chapter 7). 

• Updated guidance to the jurisdictions for potential combined application of the 
numerical water clarity criteria to shallow water habitats and submerged aquatic 
vegetation (SAV) restoration goal acreages for defining attainment of the shallow- 
water bay grass designated use (Chapter 8). 

• Guidance to the jurisdictions for determining where numerical chlorophyll a 
criteria should apply to local Chesapeake Bay and tidal tributary waters (Chapter 

9). 

Through publication by EPA as a formal addendum to the 2003 Chesapeake Bay 
Regional Criteria Guidance document, this document should be viewed by readers 
as supplemental chapters and appendices to the original published Regional Criteria 
Guidance document. The publication of future addendums by EPA is likely as 
continued scientific research and management application reveal new insights and 
knowledge to be incorporated into revisions of state water quality standards regula¬ 
tions in upcoming triennial reviews. 


chapter i 


Introduction 







3 


chapter 11 

Shortnose Surgeon Temperature 
Sensitivity Analyses 


For water column temperatures greater than 29°C, documented as stressful to short- 
nose sturgeon, EPA established a Chesapeake Bay open-water dissolved oxygen 
criterion of 4.3 mg liter -1 instantaneous minimum to protect survival of this listed 
sturgeon species (U.S. EPA 2003). An investigation was conducted to determine if 
there were water column habitats within Chesapeake Bay and its tidal tributaries 
where water column temperatures routinely exceed 29°C. States would need to apply 
the 4.3 mg liter -1 instantaneous minimum dissolved oxygen criterion in such open- 
water habitats. 

Bottom water temperature data were examined for the June through September 
period for the years 1996 through 2002 for all Chesapeake Bay tidal water quality 
monitoring stations throughout the mainstem Bay and tidal tributaries. Observations 
greater than 29°C at a station were expressed as a percentage of the total number of 
observations at the station for the 1996 through 2002 summer time period. These 
percentages were then interpolated and displayed on a map (Figure II-1). Due to the 
high density of stations within the District of Columbia’s tidal waters, this region 
was examined in greater detail (Figure II-2). 

Areas with a higher percentage of tidal water temperatures above 29°C were almost 
exclusively in the tidal fresh and oligohaline regions of the tidal tributaries. The tidal 
fresh James and Appomattox rivers had the highest percentages with 16^40 percent 
of the summer bottom water temperatures exceeding 29°C. In the Northeast, Elk, 
Bohemia, Sassafras, and tidal fresh segmemts of the Chester, Patuxent, Potomac, 
Rappahannock, Mattaponi and Pamunkey rivers, temperatures exceeded 29°C 5-15 
percent of the time. 

Examining the District of Columbia’s water quality monitoring stations’ bottom 
temperature data, it appeared that there were some stations with fairly high percent¬ 
ages of temperatures exceeding the 29°C temperature threshold (Figure II-2). But on 
closer examination, these stations were infrequently sampled and, therefore, the 
percentages were misleading. Based on a more strict evaluation of the total number 
of exceedences by station, it did not appear that elevated bottom water temperatures 


chapter ii 


Shortnose Sturgeon Temperature Sensitivity Analyses 





Temperature Threshhold Violations 
by Percent Occurence 
0% 

1-5 

mm 6-15 




Figure 11-1 . Interpolated percent occurrence of bottom water temperatures greater than 
29°C from June-September 1996-2002 at the Chesapeake Bay Water Quality Monitoring 
Program stations. Data were drawn from 48 monitoring cruises over the 7 year period. 

Source: Chesapeake Bay Water Quality Monitoring Program database. 
http://www.chesapeakebay.net/data 


chapter ii 


Shortnose Sturgeon Temperature Sensitivity Analyses 












5 



Figure 11-2. Percent occurrence of bottom water temperatures greater than 29°C from 
June- September 1996-2002 at the Chesapeake Bay Water Quality Monitoring Program 
stations located in the District of Columbia's tidal waters. 

Source: Chesapeake Bay Water Quality Monitoring Program database. 
http://www.chesapeakebay.net/data 


were high enough to trigger routine application of the 4.3 mg liter 1 instantaneous 
minimum criterion in District of Columbia tidal waters (Figure II-3). 

To further narrow down on those tidal water habitats where the temperature-based 
4.3 mg liter 1 instantaneous minimum dissolved oxygen criterion would likely 
routinely apply, the baywide data set described previously was examined for the 
number of bottom water dissolved oxygen concentrations less than 4.3 mg liter 1 
when the corresponding bottom water temperature exceeded 29°C. Over the summer 
periods of 1996 through 2002, there were a total of 20 incidences of these two condi¬ 
tions among 9 stations. Five of the stations were in the Southern Branch Elizabeth 
River and there was one station each in the tidal fresh segments of the Choptank, 
Patuxent, and Pamunkey rivers and in the oligohaline segment of the Rappahannock 
River (Figure II-4). 


chapter ii 


Shortnose Sturgeon Temperature Sensitivity Analyses 









6 



Figure 11-3. The number of times the bottom water temperatures were greater than 29°C 
from June-September 1996-2002 at the Chesapeake Bay Water Quality Monitoring 
Program stations located in the District of Columbia's tidal waters. 

Source: Chesapeake Bay Water Quality Monitoring Program database. 
http://www.chesapeakebay.net/data 


Based on these evaluations, there appear to be no widespread tidal water habitats 
exceeding the 29°C threshold, thereby requiring routine application of the 
temperature-based 4.3 mg liter 1 instantaneous minimum dissolved oxygen criteria. 
Jurisdictions are advised to evaluate water column temperatures prior to assessing 
attainment of the open-water dissolved oxygen criteria to determine if, w'here and 
when this temperature-based dissolved oxygen criterion should be applied to protect 
the open-water designated use. 


LITERATURE CITED 

U. S. Environmental Protection Agency. 2003. Ambient Water Quality Criteria for Dissolved 
Oxygen . Water Clarity' and Chlorophyll a for the Chesapeake Bay and Its Tidal Tributaries. 
EPA 903-R-03-002. Region III Chesapeake Bay Program Office, Annapolis, Maryland. 


chapter ii • Shortnose Sturgeon Temperature Sensitivity Analyses 










7 



Figure 11-4. Chesapeake Bay Water Quality Monitoring Program stations where both 
bottom water dissolved oxygen concentrations were less than 4.3 mg liter 1 and bottom 
water temperatures were greater than 29°C from June-September 1996-2002. 


Source: Chesapeake Bay Water Quality Monitoring Program database. 
http://www.chesapeakebay.net/data 


chapter ii 


Shortnose Sturgeon Temperature Sensitivity Analyses 











chapter hi 

Key Findings Published in the 
EPA ESA Shortnose Sturgeon 
Biological Evaluation 


In November of 2000, EPA initiated a voluntary informal consultation with NOAA 
National Marine Fisheries Service (NOAA Fisheries) under Section 7(a)(2) of the 
Endangered Species Act (ESA) for the issuance of guidance for Chesapeake Bay 
specific water quality criteria for dissolved oxygen, water quality and chlorophyll a. 
Upon publication of Ambient Water Quality Criteria for Dissolved Oxygen, Water 
Clarity- and Chlorophyll a for the Chesapeake Bay and Its Tidal Tributaries 
(Regional Criteria Guidance) (U.S. EPA 2003a), EPA initiated formal consultation 
with NOAA Fisheries. At the same time, EPA submitted its final Biological Evalua¬ 
tion for the Issuance of Ambient Water Quality Criteria for Dissolved Oxygen, Water 
Clarity / and Chlorophyll a for the Chesapeake Bay and its Tidal Tributaries (U.S. 
EPA 2003b) to NOAA Fisheries. This chapter provides a concise summary of key 
findings published in EPA’s biological evaluation. 1 


CONSULTATION HISTORY 

EPA sent a letter to NOAA Fisheries on November 24, 2000, requesting comments 
on the list of federally listed threatened or endangered species and/or designated crit¬ 
ical habitat for listed species under the jurisdiction of NOAA Fisheries. NOAA 
Fisheries responded in a letter dated January 8, 2001. In this letter, NOAA Fisheries 
indicated that the endangered and threatened species under its jurisdiction in the 
vicinity of the Chesapeake Bay and its tidal tributaries were: federally threatened 
loggerhead ( Caretta caretta), and endangered Kemp’s ridley ( Lepidochelys kempii ), 
green ( Chelonia my das), hawksbill ( Eretmochelys imbricata) and leatherback 
(Dermochelys coriacea) sea turtles; federally endangered North Atlantic right 


‘The entire biological evaluation document can be viewed and downloaded at: 
http://www.chesapeakebay.net/pubs/subcommittee/wqsc/BE_final.pdf 


chapter iii 


Key Findings Published in the EPA ESA Shortnose Sturgeon Biological Evaluation 











10 


(Eubalaena glacialis), humpback ( Megaptera novaeangliae ), fin ( Balaenoptera 
physalus), sei ( Balaenoptera borealis ) and sperm (Physter macrocephalas ) whales; 
and federally endangered shortnose sturgeon ( Acipenser brevirostrum). In this letter, 
NOAA Fisheries indicated to EPA that the revised dissolved oxygen criteria should 
be evaluated for effects on shortnose sturgeon survival, foraging, reproduction and 
distribution due to the lowering of dissolved oxygen criteria in the Chesapeake Bay. 

On December 20, 2002, EPA sent a letter to NOAA Fisheries requesting concurrence 
with EPA’s conclusion that the proposed criteria and refined designated uses would 
not adversely affect the listed species under NOAA Fisheries’jurisdiction. Included 
with this letter were a Biological Evaluation regarding the shortnose sturgeon and a 
copy of the draft criteria document. In a January 7, 2003 letter, NOAA Fisheries 
replied to EPA and indicated that it concurred with EPA’s conclusion as it applied to 
federally listed sea turtles and marine mammals but that NOAA Fisheries could not 
concur that the revised dissolved oxygen criteria would not adversely affect short¬ 
nose sturgeon. NOAA Fisheries provided several comments to EPA on the contents 
of the biological evaluation regarding the effects of the dissolved oxygen standards 
on shortnose sturgeon and indicated that EPA should revise the biological evaluation. 
Subsequent to receiving this letter, NOAA Fisheries and EPA staff communicated 
informally to revise the contents of the biological evaluation. 

In February 2003, several meetings and conference calls took place between EPA 
and NOAA Fisheries staff. Included in these meetings was a discussion as to how the 
formal consultation would be conducted. The complicating factor was that while 
EPA was issuing the Regional Criteria Guidance document as guidance to the states, 
the states were not obligated to adopt the criteria exactly as outlined in the Regional 
Criteria Guidance document. It was determined between EPA and NOAA Fisheries 
staff that a programmatic approach would be taken in developing an appropriate 
biological opinion. In this scenario, EPA would consult with NOAA Fisheries on the 
effects of issuing the guidance document to the states and District of Columbia since 
EPA would evaluate the States and District of Columbia’s revised water quality 
criteria in light of the Chesapeake Bay specific guidance. Then, when the states had 
developed their water quality standard regulations and submitted them to EPA, EPA 
would consult again with NOAA Fisheries on the effects of EPA approving the stan¬ 
dards proposed by the states. This type of programmatic consultation was 
particularly appropriate as the pollutant loads from each State and the District of 
Columbia mix in the Chesapeake Bay and the water quality in the Bay and its tidal 
tributaries would be a result of the combined pollutant loads from the various states 
and the District of Columbia. The consultation that is the subject of EPA’s final 
biological evaluation published April 25, 2003 and NOAA Fisheries final biological 
opinion dated April 16, 2004 serves as the first in a series of consultations that will 
take place between EPA and NOAA Fisheries on the effects of EPA’s issuing water 
quality criteria and approving water quality standards for the Chesapeake Bay and 
its tidal tributaries. 


chapter Hi 


Key Findings Published in the EPA ESA Shortnose Sturgeon Biological Evaluation 







11 


In April 2003, EPA published the final Regional Criteria Guidance document. At 
that time, EPA indicated that it had not made any irreversible or irretrievable 
commitment of resources that would foreclose the formulation or implementation of 
any reasonable and prudent alternatives to avoiding jeopardizing endangered or 
threatened species. 

On April 25, 2003, EPA submitted a final Biological Evaluation to NOAA Fisheries 
along with the published Regional Criteria Guidance and a letter requesting that 
NOAA Fisheries initiate formal consultation on the effects of the issuance of the 
dissolved oxygen criteria on shortnose sturgeon. The date April 25, 2003, serves as 
the initiation of formal consultation on the shortnose sturgeon for the issuance of the 
Regional Criteria Guidance. 

During the formal consultation process, EPA and NOAA Fisheries staff continued to 
hold discussions regarding the evaluation of the effects of EPA’s regional criteria on 
the shortnose sturgeon. On October 30, 2003, EPA management and staff traveled to 
NOAA Fisheries offices in Gloucester, Massachusetts, to provide technical informa¬ 
tion and background information on the Chesapeake Bay Program’s ambient water 
quality criteria, designated uses, monitoring program and predictive modeling 
assessments of water quality conditions of the Bay. Subsequently, communication 
between the respective staffs continued, through which EPA provided NOAA Fish¬ 
eries with requested data necessary to complete a determination analysis for the 
biological opinion. NOAA Fisheries communicated informally to the EPA that it 
concurred with EPA’s determination that the issuance of the Chesapeake Bay 
specific criteria would not affect endangered and threatened whales and that the 
issuance of the criteria for water clarity and chlorophyll a likely would beneficially 
affect federally listed sea turtles and the endangered shortnose sturgeon. However, 
NOAA Fisheries indicated that the issuance of the dissolved oxygen criteria may 
affect shortnose sturgeon and sea turtles. The effect of EPA’s issuance of the ambient 
water quality criteria on shortnose sturgeon and sea turtles was the subject of the 
consultation. 


BIOLOGICAL EVALUATION FINDINGS 

The EPA determined through consultation with the U.S. Fish and Wildlife Service 
and the NOAA National Marine Fisheries Service that the only endangered or threat¬ 
ened species under the NOAA Fisheries jurisdiction in the evaluation area that would 
potentially be affected was the endangered shortnose sturgeon ( Acipenser brevi- 
rostrum). All the other federally-listed species within the Chesapeake Bay and its 
tidal tributaries would either not be affected or would be beneficially affected by the 
issuance of the Regional Criteria Guidance. 

The EPA determined that the recommended water clarity criteria would not likely 
adversely effect the listed species evaluated. Furthermore, the EPA determined that 


chapter iii 


Key Findings Published in the EPA ESA Shortnose Sturgeon Biological Evaluation 






12 


the proposed water clarity criteria would beneficially affect preferred habitat, 
spawning areas and food sources that the listed shortnose sturgeon depends. 

The EPA determined that the recommended chlorophyll a criteria would not likely 
adversely affect the listed species evaluated. Furthermore, the EPA determined that 
the recommended chlorophyll a criteria would beneficially affect preferred habitat, 
spawning habitat and food sources on which the listed species depends. 

The EPA determined that the collective application of dissolved oxygen criteria for 
the migratory fish spawning and nursery and open-water fish and shellfish desig¬ 
nated uses were fully protective of shortnose sturgeon survival and growth for all life 
stages based on the following: 

• The migratory spawning and nursery 6 mg liter -1 7-day mean and 5 mg instanta¬ 
neous minimum criteria will fully protect spawning shortnose sturgeon. The 
February 1 through May 31 application period for the migratory spawning and 
nursery criteria fully encompasses the mid-March through mid-May spawning 
season documented previously from the scientific peer-reviewed literature. 

• The individual components of the open-water criteria protect shortnose sturgeon 
growth (5 mg liter -1 30-day mean), larval recruitment (4 mg liter -1 7-day mean) 
and survival (3.2 mg liter -1 instantaneous minimum). A 4.3 mg liter -1 instanta¬ 
neous minimum criterion applies to open waters with temperatures above 29°C 
considered stressful to shortnose sturgeon. 

• The open-water criteria applied to tidal fresh waters include a 5.5 mg liter -1 
30-day mean criterion providing extra protection of shortnose sturgeon juveniles 
inhabiting tidal freshwater habitats. 

The EPA determined that adoption of the proposed dissolved oxygen criteria into 
Maryland, Virginia, Delaware and the District of Columbia’s state water quality stan¬ 
dards and their eventual attainment would beneficially affect shortnose sturgeon 
spawning, nursery, juvenile and adult habitats and food sources by driving wide¬ 
spread nutrient loading reduction actions leading to increased existing ambient 
dissolved oxygen concentrations. EPA stated that this determination was consistent 
with and pursuant to Endangered Species Act provisions that the responsible federal 
agency—EPA in this case—use its authority to further the purpose of protecting 
threatened and endangered species (see 16 U.S.C. § 1536(a)). EPA also stated that 
its determination was also consistent with the NOAA National Marine Fisheries 
Recovery Plan for shortnose sturgeon which recommends working cooperatively 
with states to promote increased state activities to promote best management prac¬ 
tices to reduce non-point sources (NOAA National Marine Fisheries Service 1998). 

The EPA determined that adoption, implementation and eventual full attainment of 
the states’ adopted dissolved oxygen water quality standards would result in signifi¬ 
cant improvements in dissolved oxygen concentrations throughout the tidal waters to 
levels last observed consistently more than four to five decades ago in Chesapeake 
Bay and its tidal tributaries. 


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Key Findings Published in the EPA ESA Shortnose Sturgeon Biological Evaluation 



13 


The EPA recognized in the biological evaluation that dissolved oxygen criteria for 
June through September for the deep-water seasonal fish and shellfish and the deep- 
channel designated uses were at or below levels that protect shortnose sturgeon. The 
EPA believed there were strong lines of evidence that shortnose sturgeon historically 
have not used deep-water and deep-channel designated use habitats during the 
summer months due to naturally pervasive low dissolved oxygen conditions based 
on the following: 

• Published findings in the scientific literature regarding salinity preferences (tidal 
fresh to 5 ppt) and salinity tolerances (<15 ppt) clearly indicated shortnose stur¬ 
geon habitats were unlikely to overlap with the higher salinity deep-water and 
deep-channel designated use habitats. 

• The EPA concluded, based on extensive published scientific findings and in-depth 
analysis of the 1400 record U.S. Fish and Wildlife Service Reward Program data¬ 
base, that these same deep-water and deep-channel regions have not served as 
potential habitats for sturgeon during the June through September time period 
when there is a natural tendency for low dissolved oxygen conditions to occur. 

• The EPA recognized the potential limitations of the U.S. Fish and Wildlife Service 
data set. However, the EPA believed the significant extent of the capture records— 
400 stations and 1400 individuals caught—provided substantial evidence for the 
lack of a potential conflict between shortnose habitat and seasonally applied deep¬ 
water and deep-channel designated uses. 

The EPA determined that the recommended dissolved oxygen criteria for the refined 
designated uses would not likely adversely affect the listed species evaluated in this 
document. Furthermore, the EPA determined that the Chesapeake Bay dissolved 
oxygen criteria would beneficially affect critical habitat and food sources on which 
the listed species was dependent. 


BIOLOGICAL EVALUATION CONCLUSIONS 

Shortnose sturgeon are endangered throughout their entire range (NOAA National 
Marine Fisheries Service 2002). According to NOAA, in the Final Biological 
Opinion for the National Pollutant Discharge Elimination System Permit for the 
Washington Aqueduct, this species exists as 19 separate distinct population segments 
that should be managed as such. Specifically, the extinction of a single shortnose 
sturgeon population risks permanent loss of unique genetic information that is crit¬ 
ical to the survival and recovery of the species (NOAA National Marine Fisheries 
Service 2002). The shortnose sturgeon residing in the Chesapeake Bay and its tribu¬ 
taries form one of the 19 distinct population segments. 

Adult shortnose sturgeon are present in the Chesapeake Bay based on the 50 captures 
via the U.S. Fish and Wildlife Service Atlantic Sturgeon Reward Program. However, 
the presence and abundance of all life stages within the evaluation area itself are 
unknown. Preliminary published scientific evidence suggests that the shortnose 


chapter iii 


Key Findings Published in the EPA ESA Shortnose Sturgeon Biological Evaluation 




14 


sturgeon captured in the Chesapeake Bay may be part of the Delaware distinct popu¬ 
lation segment using the C & D Canal as a migratory passage. However, the NOAA 
National Marine Fisheries Service recommended that more studies utilizing nuclear 
DNA needed to be conducted before this can be proven conclusively. 

Section 9 of the Endangered Species Act and Federal regulations pursuant to section 
4(d) of the Endangered Species Act prohibit the take of endangered and threatened 
species, respectively, without special exemption. ‘Take' is defined as to harass, harm, 
pursue, hunt, shoot, wound, kill, trap, capture or collect, or to attempt to engage in 
any such conduct. ‘Harm’ is further defined by NOAA National Marine Fisheries 
Service to include any act that kills or injures fish or wildlife. Such an act may 
include significant habitat modification or degradation that actually kills or injures 
fish or wildlife by significantly impairing essential behavioral patterns including 
breeding, spawning, rearing, migrating, feeding, or sheltering. ‘Harass’ is defined by 
U.S. Fish and Wildlife Service as intentional or negligent actions that create the like¬ 
lihood of injury to listed species to such an extent as to significantly disrupt normal 
behavior patterns which include, but are not limited to, breeding, feeding or shel¬ 
tering. ‘Incidental take’ is defined as take that is incidental to, and not the purpose 
of, the carrying out of an otherwise lawful activity. 

The shortnose sturgeon recovery plan further identifies habitat degradation or loss 
(resulting, for example, from dams, bridge construction, channel dredging, and 
pollutant discharges) and mortality (resulting, for example, from impingement on 
cooling water intake screens, dredging and incidental capture in other fisheries) as 
principal threats to the species’ survival (NOAA National Marine Fisheries Service 
1998). The recovery goal is identified as delisting shortnose sturgeon populations 
throughout their range, and the recovery objective is to ensure that a minimum popu¬ 
lation size is provided such that genetic diversity is maintained and extinction is 
avoided. 

Considering the nature of the Regional Criteria Guidance , the effects of the recom¬ 
mended criteria, and future cumulative effects in the evaluation area, the issuance of 
Regional Criteria Guidance was not likely to adversely affect the reproduction, 
numbers, and distribution of the Chesapeake Bay distinct population segment in a 
way that appreciably reduces their likelihood of survival and recovery in the wild. 
This contention was based on the following: (1) the adoption of the recommended 
dissolved oxygen criteria into state water quality standards and subsequent attain¬ 
ment upon achievement of the Chesapeake Bay watershed’s nutrient loading caps 
would provide for significant water quality improvements to the tributaries to the 
Chesapeake Bay (such as the Susquehanna, Gunpowder, and Rappahannock rivers) 
where the shortnose sturgeon would most likely spawn and spend their first year of 
life; (2) the main channel of the Chesapeake Bay most likely experienced reductions 
in dissolved oxygen before large-scale post-colonial land clearance took place, due 
to natural factors such as climate-driven variability in freshwater inflow; and 
(3) there was strong evidence that shortnose sturgeon have historically not used 


chapter iii 


Key Findings Published in the EPA ESA Shortnose Sturgeon Biological Evaluation 






15 


deep-water and deep-channel designated use habitats during the summer months due 
to naturally pervasive low dissolved oxygen conditions. 

Based on the evaluations conducted in the biological evaluation, EPA concluded that 
the issuance of the Regional Criteria Guidance would not adversely affect the 
continued existence of the Chesapeake Bay district population segment of shortnose 
sturgeon. No critical habitat has been designated for this species and, therefore, none 
will be affected. In fact, the EPA believed state adoption of the criteria into water 
quality standards would directly lead to increased levels of suitable habitat for short- 
nose sturgeon. 


LITERATURE CITED 

NOAA National Marine Fisheries Serv ice. 1998. Recovery Plan for the Shortnose Sturgeon 
(Acipenser brevirostrum). Prepared by the Shortnose Sturgeon Recovery Team for the 
National Marine Fisheries Service, Silver Spring, Maryland. 

NOAA National Marine Fisheries Service. 2002. Final Biological Opinion for the Motional 
Pollutant Discharge Elimination System Permit for the Washington Aqueduct. Gloucester, 
Massachusetts. 

U.S. Environmental Protection Agency. 2003a. Ambient Water Quality' Criteria for Dissolved 
Oxygen, Water Clarity and Chlorophyll a for the Chesapeake Bay and Its Tidal Tributaries. 
EPA 903-R-03-002. Region III Chesapeake Bay Program Office, Annapolis. Maryland. 

U. S. Environmental Protection Agency. 2003b. Biological Evaluation for the Issuance of 
Ambient Water Quality Criteria for Dissolved Oxygen, Water Clarity and Chlorophyll a for 
the Chesapeake Bay and its Tidal Tributaries. Region III Chesapeake Bay Program Office, 
Annapolis, Maryland. 


chapter iii 


Key Findings Published in the EPA ESA Shortnose Sturgeon Biological Evaluation 












17 


cha pter i\/ 

Key Findings Published in the 
NOAA ESA Shortnose Sturgeon 
Biological Opinion 


In response to EPA’s submission of a biological evaluation and request for formal 
consultation under Section 7 (a)(2) of the Endangered Species Act as described in 
Chapter 2, the NOAA National Marine Fisheries Service published a biological 
opinion (NOAA National Marine Fisheries Service 2004). This chapter provides an 
extracted summary of key findings, the incidential take statement and recommended 
reasonable and prudent measures published in NOAA’s biological opinion 2 . 


CHLOROPHYLL A CRITERIA 

NOAA Fisheries determined that the chlorophyll a criteria will beneficially affect 
the food sources for several species of listed sea turtles and benefit the habitat of 
shortnose sturgeon and sea turtles (NOAA Fisheries 2004). This is based on the 
finding that the recommended Chesapeake Bay chlorophyll a criteria provide 
concentrations characteristic of desired ecological trophic conditions and protective 
against water quality and ecological impairments (U.S. EPA 2003a). When the 
chlorophyll a criteria are met, light levels and dissolved oxygen levels in the Chesa¬ 
peake Bay system should improve (U.S. EPA 2003b). The proposed chlorophyll a 
concentrations should be protective against these water quality impairments. The 
criteria should significantly improve water quality conditions in the Bay, particularly 
for underwater Bay grasses. 


WATER CLARITY CRITERIA 

NOAA Fisheries determined that shortnose sturgeon and sea turtles are expected to 
benefit from the improved water quality resulting from the adoption of the proposed 


2 The entire biological opinion document can be viewed and downloaded at: 
http://www.chesapeakebay.net/pubs/BONMFS.pdf 


chapter iv 


Key Findings Published in the NOAA ESA Shortnose Sturgeon Biological Opinion 





18 


water clarity criteria (NOAA Fisheries 2004). The endangered green sea turtle feeds 
directly on sea grasses while other sea turtle species feed on shellfish which are 
dependent on the underwater grasses for habitat. The criteria for water clarity fully 
support the survival, growth and propagation of balanced, indigenous populations of 
ecologically important fish and shellfish inhabiting vegetated shallow-water habitats 
(U.S. EPA 2003b). As the water clarity criteria will lead to increased water quality and 
an increased forage base for sea turtles, NOAA Fisheries believed that these criteria 
will beneficially affect listed sea turtles. While shortnose sturgeon are not directly 
dependent on underwater grasses, these grasses are an important part of the food chain 
making the protection of bay grasses beneficial to shortnose sturgeon as well. 


DISSOLVED OXYGEN CRITERIA 

SEA TURTLES 

After reviewing the best available information on the status of endangered and 
threatened species under NOAA Fisheries jurisdiction, the environmental baseline 
for the action area, the effects of the action, and the cumulative effects, it was NOAA 
Fisheries’ opinion that the EPA’s approval of the dissolved oxygen criteria for Chesa¬ 
peake Bay and its tidal tributaries was not likely to adversely affect loggerhead, 
leatherback, Kemp’s ridley, green, or hawksbill sea turtles. Because no critical 
habitat is designated in the action area, none will be affected by the project. 

NOAA Fisheries believed that the dissolved oxygen criteria would beneficially affect 
endangered and threatened sea turtles that may be present in the Chesapeake Bay. 
Loggerhead, Kemps ridley, leatherback and green sea turtles are likely to be present 
in the action area. The occurrence of a hawksbill turtle in the area would be a rare 
occurrence. The effect of the dissolved oxygen levels on juvenile and adult turtles 
have been assessed. As turtles are air breathers, there are not likely to be any direct 
effects to sea turtles as a result of these dissolved oxygen criteria. As the dissolved 
oxygen conditions in the Bay were expected to continually improve over the next 
several years until the nutrient and sediment enrichment goals were met, NOAA 
Fisheries anticipated that as habitat conditions improve in the Bay and habitat was 
restored, there would be an increased forage base for sea turtles. 

SHORTNOSE STURGEON 

NOAA Fisheries determined that the water clarity and chlorophyll a criteria were 
expected to improve water quality conditions in the Bay and its tidal tributaries, 
beneficially affecting all native species of the Bay including shortnose sturgeon 
(NOAA Fisheries 2004). While the dissolved oxygen levels authorized by this set of 
criteria may result in some short-term adverse effects to shortnose sturgeon, no 
chronic or lethal effects were expected. 


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Key Findings Published in the NOAA ESA Shortnose Sturgeon Biological Opinion 










19 


In addition, NOAA Fisheries determined that the adoption of the dissolved oxygen 
criteria would result in significantly improved water quality conditions in the Bay, 
elimination of anoxic zones and the improvement in the quality and quantity of 
habitat available to shortnose sturgeon as well as improving the chances for recovery 
of the Chesapeake Bay population of shortnose sturgeon and the long term sustain¬ 
ability of this population (NOAA National Marine Fisheries Service 2004). 

This determination was based on the following conclusions: 

• The effects of the ambient water quality criteria for the Chesapeake Bay and its 
tidal tributaries have been analyzed on the Chesapeake Bay population of short¬ 
nose sturgeon. While the dissolved oxygen levels authorized by this set of criteria 
may result in some short-term adverse effects to shortnose sturgeon through 
displacement or other behavioral or physiological adjustments, no chronic effects 
are expected. No lethal effects are expected as a result of the dissolved oxygen 
criteria and significant protections are being provided to essential habitats 
including deep water, spawning and nursery habitats. 

• The adoption of the dissolved oxygen criteria will result in significantly improved 
water quality conditions in the Bay, elimination of anoxic zones and the improve¬ 
ment in the quality and quantity of habitat available to shortnose sturgeon as well 
as improving the chances for shortnose sturgeon recovery in the Bay and 
improving the likelihood of long-term sustainability of this population. 

• NOAA Fisheries believes that the issuance of these criteria, as currently stated, 
would not reduce the reproduction, numbers and distribution of the Chesapeake 
Bay shortnose sturgeon population or the species as a whole in a way that appre¬ 
ciably reduces the likelihood of the species’ survival and recovery in the wild. 
This conclusion was supported by the following: (1) no lethal takes of any life 
stage of shortnose sturgeon are anticipated to occur; (2) the demonstrated ability 
of shortnose sturgeon to avoid hypoxic areas and move to areas with suitable 
dissolved oxygen levels; (3) the availability of adequate habitat with not only 
suitable temperature, salinity and depth, but suitable dissolved oxygen levels; (4) 
the seasonal nature of the anticipated effects (i.e., no effects anticipated from 
October 1-May 31 of any year); (5) adequate protection of essential spawning and 
nursery areas protecting not only spawning adults but eggs and larvae from 
hypoxic conditions; (6) the elimination of anoxic areas within the Bay; (7) a large 
portion of the deep-water areas have low temperatures and adequate dissolved 
oxygen levels allowing shortnose sturgeon to be less dependent on the deepest 
areas of the Chesapeake Bay (deep-channels) for thermal refiigia; and (8) the 
significant improvement in Bay water quality conditions and increased avail¬ 
ability of suitable habitat for all life stages of shortnose sturgeon. 

As such, it was NOAA Fisheries’ biological opinion that the approval of these 
criteria by EPA may adversely affect the Chesapeake Bay population of endangered 
shortnose sturgeon through displacement to suboptimal habitat or other behavioral 
and metabolic responses to hypoxic conditions but was not likely to jeopardize the 


chapter iv 


Key Findings Published in the NOAA ESA Shortnose Sturgeon Biological Opinion 


continued existence of the Chesapeake Bay population of shortnose sturgeon or the 
species as a whole (NOAA National Marine Fisheries Service 2004). 



INCIDENTAL TAKE STATEMENT 

Section 9 of the ESA and Federal regulations pursuant to section 4(d) of the ESA 
prohibit the take of endangered and threatened species, respectively. “Incidental 
take” is defined as take that is incidental to, and not the purpose of, the carrying out 
of an otherwise lawful activity (50 CFR 402.02). Under the terms of section 7(b)(4) 
and section 7(o)(2) of the ESA, taking that is incidental to and not intended as part 
of the agency action is not considered to be prohibited under the ESA provided that 
such taking is in compliance with the terms and conditions of this Incidental Take 
Statement. 

According to the EPA Ambient Water Quality Criteria for Dissolved Oxygen, Water 
Clarity and Chlorophyll a for the Chesapeake Bay and Its Tidal Tributaries 
{Regional Criteria Guidance ), the goal of this program is that states will adopt water 
quality standards consistent with the Regional Criteria Guidance and further imple¬ 
ment those water quality standards so that nutrient and sediment load reductions will 
be achieved by 2010. At that time, EPA expects that the dissolved oxygen criteria 
will be met for all designated uses. This Incidental Take Statement accounts for take 
that will occur before the 2010 goals are met and after the goals are met. Unless 
NOAA Fisheries revokes, modifies or replaces this Incidental Take Statement, this 
Incidental Take Statement is valid for as long as the EPA’s guidance document 
remains in effect (NOAA National Marine Fisheries Service 2004). When the States 
and the District of Columbia seek EPA approval of their dissolved oxygen criteria, 
NOAA Fisheries will verify at that time that EPA's approval of the state water quality 
criteria will also be subject to this programmatic take statement. At that time, NOAA 
Fisheries may revise this Incidental Take Statement based on a particular State’s 
implementation plan, for example to include additional terms and conditions to mini¬ 
mize the likelihood of take. 


AMOUNT AND EXTENT OF TAKE ANTICIPATED 

The proposed action is reasonably certain to result in incidental take of shortnose 
sturgeon. NOAA Fisheries stated it is reasonably certain the incidental take 
described here will occur because (1) shortnose sturgeon are known to occur in the 
action area; and (2) shortnose sturgeon are known to be adversely affected by low 
dissolved oxygen levels as low dissolved oxygen levels cause them to avoid areas, 
increase surfacing behavior, and undergo metabolic changes. Based on the evalua¬ 
tion of the best available information on shortnose sturgeon and their use of the 
Chesapeake Bay, NOAA Fisheries has concluded that the issuance of the dissolved 
oxygen criteria for seasonal deep water, deep channel and open water aquatic life 


chapter iv 


Key Findings Published in the NOAA ESA Shortnose Sturgeon Biological Opinion 






21 


uses was likely to result in take of shortnose sturgeon in the form of harassment of 
shortnose sturgeon, where habitat conditions (i.e., dissolved oxygen levels below 
those protective of shortnose sturgeon) will temporarily impair normal behavior 
patterns of shortnose sturgeon (NO A A National Marine Fisheries 2004). This 
harassment will occur in the form of avoidance or displacement from preferred 
habitat and behavioral and/or metabolic compensations to deal with short-term 
hypoxic conditions. Neither lethal takes (see below) nor harm are anticipated in any 
Bay area due to the extent of available habitat in the Bay with dissolved oxygen 
levels protective of shortnose sturgeon and the demonstrated ability of shortnose 
sturgeon to avoid hypoxic areas and move to areas with suitable dissolved oxygen 
levels. Shortnose sturgeon displaced from hypoxic areas were expected to seek and 
find suitable alternative locations within the Bay. While shortnose sturgeon may 
experience temporary impairment of essential behavior patterns, no significant 
impairment resulting in injury (i.e., “harm”) was likely due to: the temporary nature 
of any effects, the large amount of suitable habitat with adequate dissolved oxygen 
levels, and the ability of shortnose sturgeon to avoid hypoxic areas. 

As outlined in the Biological Opinion, generally shortnose sturgeon are adversely 
affected upon exposure to dissolved oxygen levels of less than 5mg liter 1 and lethal 
effects are expected to occur upon even moderate exposure to dissolved oxygen 
levels of less than 3.2mg liter -1 . Because dissolved oxygen levels are known to be 
affected by various natural conditions (e.g., tides, hurricanes or other weather events 
including abnormally dry or wet years) beyond the control of EPA or the States and 
District of Columbia and can fluctuate greatly within any given period of time, a 
monthly average dissolved oxygen level has been determined to be the best measure 
of this habitat condition within the Bay. As indicated in the Biological Opinion, an 
area that achieves a 5mg liter -1 monthly average will also achieve at least a 3.2mg 
liter -1 instantaneous minimum dissolved oxygen level. As shortnose sturgeon are 
reasonably certain to be adversely affected by dissolved oxygen conditions below 
these levels, these levels can be used as a surrogate for take. As such, for puiposes 
of this Incidental Take Statement areas failing to meet a 5mg liter -1 monthly average 
of dissolved oxygen will be a surrogate for take of shortnose sturgeon. As noted 
above, this take is likely to occur in the form of avoidance or displacement from 
preferred habitat and behavioral and/or metabolic compensations to deal with short¬ 
term hypoxic conditions (defined as harassment in this situation). The amount of 
habitat failing to meet an instantaneous minimum of 3.2mg liter -1 could be used as 
a surrogate for lethal take of shortnose sturgeon; however, due to limitations of the 
model developed by EPA (U.S. EPA 2003c), the amount of habitat failing to reach a 
3.2mg liter -1 instantaneous minimum could not be modeled. However, an analysis of 
the likelihood of lethal take can be based on the amount of habitat failing to reach a 
3mg liter -1 monthly average (which would also likely be failing to meet a 3.2mg 
liter -1 instantaneous minimum). While a small portion of the Bay will fail to meet 
the 3 mg liter -1 monthly average, shortnose sturgeon are likely to be able to avoid 
these areas. Lethal effects are only expected to occur after at least 2-4 hours of expo¬ 
sure to dissolved oxygen levels of less than 3.2mg liter -1 , and this is not likely to 


chapter iv 


Key Findings Published in the NOAA ESA Shortnose Sturgeon Biological Opinion 


22 


occur given the mobility of shortnose sturgeon and the availability of suitable 
habitat. Therefore, no lethal take is expected to occur. 

The probability of lack of attainment of dissolved oxygen levels protective of short- 
nose sturgeon when the 2010 sediment and nutrient reduction goals are met has been 
modeled by EPA (U.S. EPA 2003c) and was the basis for determining the extent of 
take anticipated. As such, take levels can be determined for each of the designated 
uses where take is anticipated (open water, deep-water and deep-channel). As indi¬ 
cated in the biological opinion, take is likely to occur only in the summer months 
(June 1-September 30). Based on the analysis documented in the accompanying 
biological opinion, the area of the Bay designated uses that fail to meet a 5mg liter 1 
monthly average dissolved oxygen level can be used as a surrogate for take of short- 
nose sturgeon by harassment. As shortnose sturgeon are benthic fish, the modeling 
runs done for the bottom layer of the Bay have been used to determine the extent of 
take. To further refine this analysis, the “tolerate” habitat threshold has been used; 
that is, the estimate of area that will have temperatures <28°C, salinity <29 ppt and 
depth <25 meters which can be reasonably expected to be the areas of the Bay where 
shortnose sturgeon may be present in the summer months (U.S. EPA 2003c). 

Despite the use of the best available scientific and commercial data, NOAA Fisheries 
cannot quantify the precise number of fish that are likely to be taken. Because both 
the distribution of shortnose sturgeon throughout the Bay and the numbers of fish 
that are likely to be in an area at any one time are highly variable, and because inci¬ 
dental take is indirect and likely to occur from effects to habitat, the amount of take 
resulting from harassment is difficult, if not impossible, to estimate. In addition, 
because shortnose sturgeon are aquatic species who spend the majority of their time 
on the bottom and because shortnose sturgeon are highly mobile while foraging in 
the summer months, the likelihood of discovering take attributable to this proposed 
action is very limited. In such circumstances, NOAA Fisheries uses a surrogate to 
estimate the extent of take. The surrogate must be rationally connected to the taking 
and provide an obvious threshold of exempted take which, if exceeded, provides a 
basis for reinitiating consultation. For this proposed action, the spatial and temporal 
extent of the area failing to meet dissolved oxygen standards protective of shortnose 
sturgeon provides a surrogate for estimating the amount of incidental take. 

EXTENT OF TAKE FROM 2004-2009 

Using data provided by EPA, the extent of take occurring from the time of the adop¬ 
tion of the guidance 3 could be estimated. As habitat conditions in the Bay are 
expected to improve over time as interim measures are achieved before the 2010 
goals are met, it is reasonable to assume that this surrogate level of take will decrease 


3 Adoption of the guidance by the states and District of Columbia and approval by EPA is expected to 
occur in 2004 and 2005. 


chapter iv 


Key Findings Published in the NOAA ESA Shortnose Sturgeon Biological Opinion 



over time. Using the EPA model of dissolved oxygen conditions in 2000 in the 
bottom layer of habitat that was rated “tolerate” (see above) the following conditions 
were observed: 


23 


Designated Use 

Percent of area failing to meet 5mg liter 1 monthly 
averaqe 2004-2009 (see U.S. EPA 2003c) 

Open Water 

9.2 

Deep Water 

47.3 

Deep Channel 

78.3 


Each year in the summer months, no more than the above percentages of the partic¬ 
ular designated use areas were expected to fail to meet a 5 mg liter 1 monthly 
average dissolved oxygen level between 2004 and 2009. The extent of take would be 
limited to those percentages of each designated use area in the Bay. As such, for the 
period 2004 through 2009, NOAA Fisheries would consider take to have been 
exceeded when upon review of the annual monitoring data, NOAA Fisheries was 
able to determine that for the preceding summer, the dissolved oxygen data for any 
30 days during the June 1-September 30 time frame indicate that any of the desig¬ 
nated use area failed to meet the above goals. 

EXTENT OF TAKE IN 2010 AND BEYOND 

Using the EPA model, the extent of take anticipated in 2010 and beyond can be 
determined. Using the EPA model of dissolved oxygen conditions anticipated 
when the 2010 nutrient and sediment reduction goals were met and using the bottom 
layer of habitat that is rated “tolerate” (see above) the following conditions were 
anticipated: 


Designated Use 

Percent of area failing to meet 5mg liter 1 monthly 
average 2010 and beyond (see U.S. EPA 2003c) 

Open Water 

5.7 

Deep Water 

33.0 

Deep Channel 

65.9 


As conditions were expected to be improving over time, no more than the above 
percentages of the particular habitats were expected to fail to meet a 5mg liter 1 
monthly average dissolved oxygen level in 2010 and beyond. As such, for the period 
of 2010 and beyond, NOAA Fisheries will consider take to have been exceeded 
when upon review of the annual monitoring data, NOAA Fisheries was able to deter¬ 
mine that for the preceding summer, the dissolved oxygen data for any 30 days 
during the June 1-September 30 time frame indicate that any of the designated use 
area failed to meet the above goals. 


REASONABLE AND PRUDENT MEASURES 

Reasonable and prudent measures are those measures necessary and appropriate to 
minimize incidental take of a listed species. For this particular action, however, it is 


chapter iv 


Key Findings Published in the NOAA ESA Shortnose Sturgeon Biological Opinion 









24 


not possible to design reasonable and prudent measures that are necessary and 
appropriate to minimize take, because the best available science has demonstrated 
that the EPA criteria are the limit of feasibility based on current technology. The 
purpose of the reasonable and prudent measure below is to monitor environmental 
conditions in the Bay and to monitor the level of take associated with this action. In 
order to monitor the level of incidental take, monitoring of dissolved oxygen and 
accompanying temperature conditions in the Bay must be completed each summer. 

In order to be exempt from the prohibitions of section 9 of the ESA, the EPA must 
comply with the following terms and conditions, which implement the reasonable 
and prudent measure described above and outline the required reporting require¬ 
ments. These terms and conditions are non-discretionary. 

1. By April 1 of each year (beginning in 2005), EPA shall provide an annual report 
to NOAA Fisheries outlining the progress towards nutrient and sediment load 
reductions, including a discussion of any best management practices or other 
strategies put in place to achieve the target nutrient and sediment load reductions. 

2. EPA shall continue using the results of the Chesapeake Bay Interpolator to 
extrapolate measured data to assess water quality conditions in the Bay. The 
Chesapeake Bay Interpolator extrapolates water quality concentrations 
throughout the Chesapeake Bay and/or tributary rivers from water quality meas¬ 
ured at point locations. The purpose of the Interpolator is to assess water quality 
concentrations at all locations in the 3-dimensional water volume or as a 2- 
dimensional layer. The results from the Interpolator will be used by EPA to 
develop an annual report (see below). 

3. By April 1 of each year (beginning in 2005), EPA shall provide an annual report 
to NOAA Fisheries on water quality conditions in the Bay, including tempera¬ 
ture, dissolved oxygen, depth and salinity. The data provided will express actual 
monitoring data in volumetric figures (cubic kilometers) as well as bottom 
habitat area (squared kilometers) extrapolated from the Chesapeake Bay Inter¬ 
polator. This report should include information on the percent of each designated 
use that failed to meet the 5mg liter -1 monthly average for June, July, August and 
September of the preceding year. 

By April 30, 2010, EPA shall submit a report to NOAA Fisheries assessing the 
dissolved oxygen condition in the Bay which highlights the dissolved oxygen condi¬ 
tions in the Bay during the June 1-September 30 time frame for each of the years 
2004 through 2009. In this report, EPA will determine the percent of each designated 
use that failed to attain a 5mg liter -1 monthly average. Included in this report will be 
an analysis of the likely causes of failures (i.e., weather events, point sources). 


LITERATURE CITED 

NOAA National Marine Fisheries Service. 2004. National Marine Fisheries Ser\'ice Endan¬ 
gered Species Act Biological Opinion—Ambient Water Quality 1 Criteria for Dissolved 


chapter iv 


Key Findings Published in the NOAA ESA Shortnose Sturgeon Biological Opinion 



25 


Oxygen, Water Clarity and Chlorophyll a for the Chesapeake Bay and Its Tidal Tributaries. 
F/NER/2003/00961. Northeast Region, Gloucester. Massachusetts. 

U.S. Environmental Protection Agency. 2003a. Ambient Water Quality Criteria for Dissolved 
Oxygen, Water Clarity> and Chlorophyll a for the Chesapeake Bay and Its Tidal Tributaries. 
EPA 903-R-03-002. Region Ill Chesapeake Bay Program Office, Annapolis, Maryland. 

U.S. Environmental Protection Agency. 2003b. Biological Evaluation for the Recommended 
Ambient Water Quality> Criteria and Designated Uses for the Chesapeake Bay and its Tidal 
Waters Under the Clean Water Act Section 117. Region III Chesapeake Bay Program Office, 
Annapolis, Maryland. 

U.S. Environmental Protection Agency. 2003c. Unpublished Analysis of Shortnose Sturgeon 
Habitat Quality Preferences under Monitoring Program Observed data from 1985-1994 and 
Water Quality Modeling Estimated Water Quality Conditions for 2010. Region III Chesa¬ 
peake Bay Program Office. Annapolis, Maryland. 


chapter iv 


Key Findings Published in the NOAA ESA Shortnose Sturgeon Biological Opinion 













27 


chapter \/ 

Guidance for Attainment 
Assessment of Instantaneous 
Minimum and 7-Day Mean 
Dissolved Oxygen Criteria 


BACKGROUND 

As published in the Ambient Water Quality Criteria for Dissolved Oxygen, Water 
Clarity and Chlorophyll a for the Chesapeake Bay and Its Tidal Tributaries (U.S. 
EPA 2003), it is accepted that concentration minima need to be defined, which if 
exceeded for some defined (short) duration result in lethal or other adverse effects. 
Instantaneous minimum criteria have been derived and published for protection of 
each of the five tidal water designated uses. A 1 -day mean dissolved oxygen crite¬ 
rion was also determined to be necessary for the protection of the deep-water 
designated use. In addition, a 7-day mean criterion has been derived for protection 
of the open-water designated use (U.S. EPA 2003). 

However, it is also acknowledged that assessing the attainment status of these criteria 
requires data collections at temporal and spatial scales that are simply not practicable 
nor sustainable across all Chesapeake Bay and tidal tributary waters. To address this 
issue, there are ongoing efforts to develop statistical methods to estimate attainment 
of these dissolved oxygen criteria using a synthesis of: 1) seasonal and inter-annual 
patterns found in the long term, low-frequency, spatially-limited monitoring data; 2) 
the short-term patterns of temporal variability found in high-frequency, spatially 
uneven ‘buoy’ data; and 3) the small-interval patterns of variability observed in data 
records generated through the ‘data-flow’ and ‘scan-fish’ sampling devices. 


CURRENT STATUS 

These methods are in the exploratory and trial application phases. However, we can 
still address the question of how best to assess attainment of these criteria given the 
almost two-decade record of dissolved oxygen concentrations for Chesapeake Bay 
tidal waters. First, there are some Chesapeake Bay Program segments, such as the 
deep-channel mid-Chesapeake Bay mainstem segments and the lower Potomac 


chapter v 


Guidance for Attainment Assessment of Instantaneous Minimum and 7-Day Mean Dissolved Oxygen Criteria 




28 


River, whose hypoxic/anoxic conditions are of long standing and whose dynamics 
are well enough understood to be modeled mathematically and relatively precisely. 
There are other segments that have long term monthly and twice monthly dissolved 
oxygen concentration records whose station coverage is considered to represent the 
whole segment adequately or at least areas most likely to have dissolved oxygen 
concentrations below saturation levels. The Chesapeake Bay Program partners have 
previously demonstrated (see Chesapeake Bay Dissolved Oxygen Goal for Restora¬ 
tion of Living Resource Habitats ; Jordan et al. 1992) that relatively good predictive 
models can be developed for segments that suffer hypoxia at some regular frequency 
and so far have demonstrated no long term trend in dissolved oxygen concentrations. 
These models produce estimates of the percent of time the segment depth is below 
some specified concentration. These monitoring data-based models reflect only 
daytime measurements, but can be enhanced (and validated) by the in-situ contin¬ 
uous records from the buoy deployments. 

The remaining segments not characterized above are those segments where the long¬ 
term fixed monitoring stations, sampled on a monthly to twice-monthly basis, do not 
well represent dissolved oxygen conditions elsewhere in the segment. Typically 
these segments have a moderately deep channel with flanking nearshore areas of 
significant size. In these segments, tidal pulses from downstream, inflows from 
upstream, and local land-based influences vary in their dominance, and the current 
long-term water quality monitoring data do not capture ephemeral events or the near¬ 
shore conditions very well. The new shallow water monitoring component of the 
larger Chesapeake Bay Water Quality Monitoring Program is designed to generate 
the additional data necessary to assess criteria attainment in these segments. The 
Chesapeake Bay Program partners are now accumulating such data for a growing 
number of Chesapeake Bay Program segments. 


ASSESSMENT OF INSTANTANEOUS MINIMUM 
CRITERIA ATTAINMENT FROM MONTHLY MEAN DATA 

By overlaying information from the buoy data about diurnal variability and the 
frequency of common hypoxic events, such as those caused by phytoplankton bloom 
respiration and decay, pycnocline tilting, etc., on top of the long-term fixed-station 
monitoring data record, we can better understand the relationship between attain- 
ment/non-attainment of the 30-day mean and instantaneous minimum criteria. The 
reader should keep several things in mind. The temporal record of the long-term, 
fixed-station monitoring program is considered “low-frequency” relative to the high 
frequency record of the “continuous” data record from the buoy deployments. The 
available continuous records chronicle a few days to months of a single year. Each 
measurement is closely related to the previous and next measurement, providing a 
detailed record of the dissolved oxygen response to the specific conditions of that 
period. These buoy data records are measuring conditions at a single fixed point in 
the water column, usually about a meter off the bottom in these data sets. The sensors 


chapter v 


Guidance for Attainment Assessment of Instantaneous Minimum and 7-Day Mean Dissolved Oxygen Criteria 



29 


are fixed, but the water mass moves past, back and forth with the tide and the various 
complexities of the local riverine and estuarine circulation. The majority of the avail¬ 
able buoy data were collected through buoy deployments that were sited using 
stratified random design considerations or to answer location-specific questions, but 
not directly to address the relationship between instantaneous minimum and monthly 
mean concentrations. 

In contrast, the long term monitoring program includes a vast network of stations 
sited specifically to represent overall water quality conditions of the 78 Chesapeake 
Bay Program segments. The low-frequency monitoring record captures a snapshot of 
conditions only once or twice a month, but that series of snapshots now extends over 
an 19-year period and is ongoing. Each snapshot consists of synoptic measurements 
forming a relatively dense three-dimensional spatial data grid. The grid is formed 
horizontally by the network of mainstem and tidal tributary monitoring stations and 
vertically by the dissolved oxygen profiles measured at 1- to 2-meter intervals from 
water column surface to bottom water-sediment interface. A single summer ‘snap¬ 
shot cruise' typically includes over a thousand individual dissolved oxygen 
concentration measurements. 

REFERENCE POINTS WITH RESPECT TO DEPTH 

Dissolved oxygen levels are strongly related to depth, bathymetry, and flow and 
circulation patterns. Table V-l provides information that helps to decide how repre¬ 
sentative the long-term fixed-station monitoring data and the continuous buoy data 
records are of their respective Chesapeake Bay Program segment. Table V-l presents 
segment volume, the depth of the Chesapeake Bay Water Quality Program moni¬ 
toring station(s) in the segment, and the segment-wide bottom depth distribution i.e., 
maximum depth, the depth encompassing 90 percent, 75 percent, 50 percent (the 
median) and 25 percent of the bottom depths, as well as the minimum depth. 

DATA ASSEMBLAGE AND MANIPULATION 

Table V-2 lists the 147 continuous buoy data sets available for analysis through the 
Chesapeake Information Management System (partner network of Chesapeake Bay 
data and information servers), latitude/longitude location information, the time interval 
between measurements, the total duration of deployment, water depth and depth of the 
sensor at the site and in what depth category the sensor depth falls, based on the depth 
distributions listed in Table V-l. The list of data sets has been categorized according to 
Chesapeake Bay Program segment so that it is obvious which segments have or do not 
have such high frequency information available for evaluating and establishing the 30- 
day mean and instantaneous minimum concentration relationship. 


chapter v 


Guidance for Attainment Assessment of Instantaneous Minimum and 7-Day Mean Dissolved Oxygen Criteria 


30 


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chapter v 


Guidance for Attainment Assessment of Instantaneous Minimum and 7-Day Mean Dissolved Oxygen Criteria 


** = No bathymetry data available. Estimated volume is based on the count of Chesapeake Bay Interpolator cells of 
dimension 1 kilometer x 1 kilometer x 1 meter. 




32 


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Guidance for Attainment Assessment of Instantaneous Minimum and 7-Day Mean Dissolved Oxygen Criteria 














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35 


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Guidance for Attainment Assessment of Instantaneous Minimum and 7-Day Mean Dissolved Oxygen Criteria 












DESIGNATED USE ASSIGNMENTS 



Both the low frequency long-term fixed station and the continuous buoy data records 
were assessed relative to the published Chesapeake Bay dissolved oxygen criteria. 
The criteria are specific to different designated uses and, therefore, seasons (U.S. 
EPA 2003). With very few exceptions, the buoy data currently available were 
summer deployments (June-September). One exception begins at the end of April; 
this one and a couple of other deployments extend through October, and one extends 
to November. 

Each data record was assigned to a designated use within a Chesapeake Bay Program 
segment based on following method. Using the Chesapeake Bay Water Quality Moni¬ 
toring Program data, the depth of the upper and lower pycnoclines, if any, were 
calculated for each station for each cruise date and the segment averages for the 
month/year were determined. These segment-averaged pycnocline depths were then 
merged by corresponding dates with the buoy sensor depths in those segments where 
deep-water and deep-channel designated uses apply. It is important to remember that 
pycnocline depths may be fairly stable in some areas, but changeable and ephemeral 
in others, even within the same segment. An average pycnocline depth for the month 
may have a lot of variability around it, and thus the designated use assignments for 
some buoy data records may not be correct. Where the buoy dissolved oxygen 
concentrations suggested an incorrect assignment, the monitoring data at stations and 
dates nearest in time and space to the buoy deployment were examined in detail and 
any appropriate changes to the designated use assignment were made accordingly. 

FINDINGS 

Day/Night Differences In Dissolved Oxygen Concentration 

A commonly expressed concern about the Chesapeake Bay Water Quality Moni¬ 
toring Program’s dissolved oxygen data is that they reflect daytime dissolved oxygen 
levels, the time period when active photosynthesis by algae, and consequent gener¬ 
ation and introduction of new oxygen into the water column, may mask lower 
nighttime concentrations. To address this concern, the buoy data were partitioned 
into day (defined as 9:00 AM to 5:00 PM) and night (defined as after 5:00 PM to 
before 9:00 AM) periods and summarized. Table V-3 provides the following statis¬ 
tics for the day and night periods: minimum concentration, the concentration of the 
lowest 1 percent of measurements, the lowest 10 percent, the median, mean, standard 
deviation, and coefficient of variation, separately for day and night periods each 
month, and the number of measurements taken in that month. 

Table V-4 pools all the continuous buoy data for a station’s designated use to show 
average day/night differences at each site. The difference between the daytime mean, 
minimum, 1 percent, etc. and the equivalent nighttime statistic was computed for 
each date of deployment and the means of the daily day-night differences are shown 
in the table (difference = daytime concentration minus nighttime concentration). 


chapter v 


Guidance for Attainment Assessment of Instantaneous Minimum and 7-Day Mean Dissolved Oxygen Criteria 







37 





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chapter v 


Guidance for Attainment Assessment of Instantaneous Minimum and 7-Day Mean Dissolved Oxygen Criteria 










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chapter v 


Guidance for Attainment Assessment of Instantaneous Minimum and 7-Day Mean Dissolved Oxygen Criteria 













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chapter v • Guidance for Attainment Assessment of Instantaneous Minimum and 7-Day Mean Dissolved Oxygen Criteria 


46 


With some clear exceptions, the day-night concentration differences in these buoy 
data are small. Back River (segment BACOH), a tidal river known to be stressed by 
discharges from a large urban sewage treatment facility, exhibits the largest day- 
night difference in mean and median concentrations: -2.24 mg liter' 1 and -4.51 mg 
liter 1 , respectively (Table V-4). Note that here the nighttime concentration is higher 
than during the daytime, which seems counterintuitive. But, in fact, the average 
day/night difference in the daily means and medians is almost always negative in this 
table. A buoy site in the lower Potomac River (POTMH) and one in upper Potomac 
River (POTTF) showed day-night differences greater than 1 mg liter 1 in the daily 
mean or median or both, but all other sites showed differences less than 1 mg liter -1 . 

The average day-night differences in the daily minimum concentration and lowest 
1 percent value were similarly generally small, but with more sites exhibiting day- 
night differences in excess of 1 mg liter -1 : mesohaline Patapsco River (PATMH), 
tidal fresh (POTTF) and mesohaline (POTMH) Potomac River, tidal fresh James 
River (JAMTF), middle central and lower western mainstem Chesapeake Bay 
segments CB4MH and CB6PH, respectively, and Tangier Sound (TANMH). In 
contrast to the findings for the daily mean and median, the concentration minima and 
lowest 1 percent were generally higher in the daytime than at night. 

30-Day Mean and Instantaneous Minimum Criteria Attainment 

Table V-5 shows how the continuous dissolved oxygen measurements stack up 
against the corresponding designated use dissolved oxygen criteria. The dissolved 
oxygen criteria are to be assessed for each segment/designated use separately. Thus, 
in this analysis, the day and night measurements are pooled and the mean, 1 percent 
concentration and other statistics are calculated within month, if the data record 
extends over multiple months. Asterisks flag the continuous buoy data records where 
the 30-day mean criterion is not achieved (i.e., monthly mean dissolved oxygen 
concentration is lower than the applicable criterion) or where the measured 1 percent 
dissolved oxygen concentration is lower than the instantaneous minimum criterion. 

Looking down the columns in Table V-5 labeled “30-day Mean” and “Instantaneous 
Minimum” under the heading “Criterion Not Achieved”, it can be seen frequently 
that if the 30-day mean criterion was achieved, the instantaneous minimum criterion 
was also achieved. Conversely, if the 30-day mean criterion was not achieved, the 
instantaneous minimum criterion also was not achieved. Further, if only one 
dissolved oxygen criterion was not achieved, then it was usually the instantaneous 
minimum criterion that was not achieved. 

Table V-6 summarizes the criteria achieved/not achieved rate by segment and desig¬ 
nated use and Table V-7 pools the Table V-6 findings by designated use. For the 
open-water designated use, in 80 out of 94 cases (—85 percent), if the 30-day mean 
criterion was achieved/not achieved, then the same was the case for the instantaneous 
minimum criterion. In deep-water designated use habitats, this condition was true in 
15 out of 26 cases (~57 percent). The diversity of buoys deployed in deep-channel 
designated use habitats is too small for drawing very specific conclusions at this time. 

chapter v • Guidance for Attainment Assessment of Instantaneous Minimum and 7-Day Mean Dissolved Oxygen Criteria 




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Guidance for Attainment Assessment of Instantaneous Minimum and 7-Day Mean Dissolved Oxygen Criteria 








Table V-6. Summary of continuous dissolved oxygen buoy data achievement/non-achievement of the applicable 30-day mean 
and instantaneous minimum dissolved oxygen criteria by Chesapeake Bay Program segment by designated use. 


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Table V-7. Summary of continuous dissolved oxygen buoy data achievementynon-achievement of the applicable 30-day mean and 
instantaneous minimum dissolved oxygen criteria summarized Bay-wide by designated use. 



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chapter v • Guidance for Attainment Assessment of Instantaneous Minimum and 7-Day Mean Dissolved Oxygen Criteria 









52 


Predicting the Lowest 1 Percent Concentration From The Mean 

Down the left side of Figure V-l are plots of the 1 percent measured dissolved 
oxygen concentration versus the measured monthly mean concentration for each 
designated use (all buoy records parsed by month and pooled within designated use). 
Down the right side of Figure V-l are plots of the same sets of measurements only 
for an individual segment, CB4MH as an example, where multiple buoys or records 
including multiple months were available. Both solid circles and open triangles are 
displayed on the plots. The circles are the observed 1 percent concentration data; the 
triangles are concentrations predicted by a simple regression model including the 
observed monthly mean and the coefficient of variation. In these examples, the 
prediction model does pretty well because of the relative large number of observa¬ 
tions and thus the very good estimate of the monthly mean and 1 percent 
concentrations, as well as the close relationship of each observation to the next. As 
the number of available continuous buoy data records increases for a wider array of 
segments and designated uses, the Chesapeake Bay Program partners should be in a 
position to develop a more generalized model for designated uses by segment that 
would enable the user to predict the 1 percent concentration from the monthly means 
obtained from the long-term fixed-station monitoring data. 

One question still under investigation is how well those observed monthly means 
compare to the means obtained from the continuous buoy data records. Figure V-2, 
which shows the fixed station twice monthly monitoring data and semi-continuous 
buoy data plotted together, provides some current insights into answering this ques¬ 
tion. Down the left side of Figure V-2 are plots of the observed 1 percent 
concentrations versus observed monthly mean dissolved oxygen concentrations 
(June-September) obtained from fixed station monitoring data and plotted for open- 
water, deep-water and deep-channel designated uses in segment CB4MH. Down the 
right side of Figure V-2 are the plots from the continuous buoy data for CB4MH. The 
vertical and horizontal reference lines cutting each graph into 4 quadrants represent 
the 30-day mean and instantaneous minimum dissolved oxygen criteria concentra¬ 
tions. Again, a regression model using the mean and coefficient of variation of the 
monitoring data has been used to predict the 1 percent concentration. As illustrated 
in Figure V-l, solid circles represent the observed concentrations and open triangles 
represent the predicted concentrations. As expected from the fixed station moni¬ 
toring data, the fit of predicted to observed is not as tight as with the buoy data. These 
regression models can be improved with the addition of more explanatory variables. 
The point is that in some, possibly many segments, the relationship of the monthly 
mean with the 1 percent concentration evidenced in monitoring data is similar to that 
found in the buoy data records. The regression models output illustrated in Figures 
V-l and V-2 can be improved by including other explanatory variables to better 
predict the variability detected and quantified in the buoys. 

Figure V-3 shows similar plots of the 1 percent concentration versus the monthly 
mean obtained from monitoring data in various other example segments. Note how 
tight the relationship is in segment BOHOH (Bohemia River) in contrast to the 


chapter v 


Guidance for Attainment Assessment of Instantaneous Minimum and 7-Day Mean Dissolved Oxygen Criteria 





53 



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oxygen concentration as measured by sensors on individual buoys. Plots on left side show patterns of dissolved 
oxygen concentration data pooled across Chesapeake Bay Program segments within open-water, deep-water and 
deep-channel uses. Plots on the right side show patterns of dissolved oxygen concentration data from middle cen¬ 
tral Chesapeake Bay, segment CB4MH. Circles are observed dissolved oxygen concentration data; open triangles are 
dissolved oxygen concentrations predicted by the regression model: 1 percent dissolved oxygen concentration as a 
function of monthly mean dissolved oxygen and the coefficient of variation. 


Source: Chesapeake Bay Water Quality Monitoring Program database. 
http://www.chesapeakebay.net/data 


chapter v 


Guidance for Attainment Assessment of Instantaneous Minimum and 7-Day Mean Dissolved Oxygen Criteria 











































54 


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-2 0 2 4 6 8 10 12 

Monthly Mean Dissolved Oxygen Concentration 


CB4MH Deep—Channel 
Buoy Data 




-2 0 2 16 8 10 
Monthly Mean Dissolved Oxygen Concentration 


12 


Figure V-2. Plots of monthly mean dissolved oxygen concentration (mg liter 1 ) versus the 1 percentile dissolved 
oxygen concentration in middle central Chesapeake Bay, segment CB4MH. Plots on left side show the pattern of 
observed dissolved oxygen concentration data from the Chesapeake Bay Water Quality Monitoring Program 
(May-September 1985-2003). Plots on right side show observed dissolved oxygen data from segment CB4MH as 
measured during various buoy deployments. Circles are observed dissolved oxygen concentrations; open triangles 
are dissolved oxygen concentrations predicted by the regression model: 1 percent dissolved oxygen concentration 
as a function of monthly mean dissolved oxygen concentration and coefficient of variation. 

Source: Chesapeake Bay Water Quality Monitoring Program database. 
http://www.chesapeakebay.net/data 


chapter v 


Guidance for Attainment Assessment of Instantaneous Minimum and 7-Day Mean Dissolved Oxygen Criteria 


















































55 


s c 

If 

J g 

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v c 
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10 

8 

6 

4 

2 

0 

-2 


CB1TF Open—Water 







-2 0 2 4 $ 8 10 12 

Monthly Mean Dissolved Oxygen Concentration 


C87PH Open—Water 







-2 0 2 4 $ 8 10 

Monthly Mean Dissolved Oxygen Concentration 


12 


MAGMH Open—Water 


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4> 

O) 


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to 

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0) 

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8 | 


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Monthly Mean Dissolved Oxygen Concentration 


CB7PH Deep-Water 



• 

• * 

V 

Cl 



-2 0 2 4 6 8 10 

Monthly Mean Dissolved Oxygen Concentration 


12 


YRKPH Deep-Water 



Figure V-3. Plots of monthly mean ambient dissolved oxygen concentration versus the one percentile dissolved 
oxygen concentrations in several example Chesapeake Bay Program segments: the northern Chesapeake Bay 
(CB1TF), Bohemia River (BOHOH), open-water and deep-water lower eastern Chesapeake Bay (CB7PH), Magothy 
River (MAGMH) and the lower York River (YRKPH). These graphics show patterns of dissolved oxygen data from the 
Chesapeake Bay Water Quality Monitoring Program from May-September 1985-2003. Circles are observed dissolved 
oxygen concentration data; open triangles are dissolved oxygen concentrations predicted by the regression model: 

1 percent dissolved oxygen concentration as a function of monthly mean dissolved oxygen concentration and 
coefficient of variation. 

Source: Chesapeake Bay Water Quality Monitoring Program database. 
http://www.chesapeakebay.net/data 


chapter v 


Guidance for Attainment Assessment of Instantaneous Minimum and 7-Day Mean Dissolved Oxygen Criteria 


















































56 


scatter of points in the plot for segment MAGMH (Magothy River), indicating large 
between-segment differences in variability and predictability. 

The plots in Figure V-3 illustrate the differences among segments in their patterns of 
criteria non-achievement. The four quadrants bounded by the reference lines in the 
plots represent the four possible results from a two-criteria achievement assessment. 
Let the quadrants be numbered clockwise 1 through 4, beginning with the upper 
right hand quadrant. Any data points in quadrant 1 achieve both the 30-day mean and 
instantaneous minimum criteria. Data points in quadrant 2 achieve the 30-day mean 
criterion, but do not achieve the instantaneous minimum criterion. Data points in 
quadrant 3 do not achieve both the 30-day mean and instantaneous minimum 
criteria. Data points in quadrant 4 achieve the instantaneous minimum criterion, but 
do not achieve the 30-day mean criterion. In a fully restored Chesapeake Bay, one 
would expect that most data points would fall in quadrant 1. In impaired segments, 
where low dissolved oxygen conditions are frequent or chronic, one would expect 
most data points to fall in quadrant 3. In segments where low dissolved oxygen 
events are episodic, ranging from occasional to frequent, one would expect a dense 
population of data points in quadrant 2. And, where dissolved oxygen concentrations 
are chronically reduced, but really low dissolved oxygen concentrations are rare, 
then one would expect some data points in quadrant 4. 

Providing plots such as those presented in Figure V-3 for each designated use for 
every segment is impractical for this document. Instead, Table V-8 shows the number 
of points in a representative data set that would be in each quadrant, if the data were 
plotted as in Figure V-3 using the summer only data from a recent 10-year period: 
June-September, 1993-2002. 

There are 66 segments that have only open-water designated uses. A total of 28 of 
these segments achieve both the 30-day mean and instantaneous minimum criteria, 
i.e., which have all their data points in quadrant 1 and none or only one data point in 
the other quadrants. These segments are marked with a single asterisk in Table V-8. 
In these open-water only segments, assessment of attainment of the instantaneous 
minimum criterion can be directly based on assessment of attainment of the 30-day 
mean criterion (Table V-9). 

A total of 18 segments with only open-water designated uses had the vast majority 
(greater than two-thirds) of their data points in either quadrant 1 or quadrant 3. These 
segments are marked with double asterisks in Table V-8. The assessment of attain¬ 
ment of the instantaneous minimum criterion can be directly based on assessment of 
attainment of the 30-day mean criterion in these segments (Table V-9). 

In five segments with only open-water designated uses there were sufficient data 
points in quadrant 2 indicating a much higher occurrence where the 30-day mean 
criterion was achieved yet the instantaneous minimum criterion was not achieved. 
These segments are marked with a single dash in Table V-8. These five segments 
were: upper Chesapeake Bay (CB20H), Magothy River (MAGMH), Severn River 
(SEVMH), Mobjack Bay (MOBPH) and Little Choptank River (LCHMH). Users 


chapter v 


Guidance for Attainment Assessment of Instantaneous Minimum and 7-Day Mean Dissolved Oxygen Criteria 




57 


Table V-8. Characterization of the Chesapeake Bay Program segments based on 

occupied quadrants in a plot of the 1 percent dissolved oxygen concentration 
versus observed monthly mean dissolved oxygen concentration 1 . 


Number of Data Points By Quadrant by Designated Use 


CBP 

Segment 


Open 

-Water 



Deep-Water 



Deep-Channel 


1 

2 

3 

4 

1 

2 

3 

4 

1 

2 3 

4 

CB1TF* 

39 

0 

0 

0 








CB20H- 

12 

19 

8 

0 








CB3MH 

38 

2 

0 

0 

2 

34 

4 

0 

3 

17 18 

0 

CB4MH 

35 

5 

0 

0 

1 

8 

31 

0 

2 

2 36 

0 

CB5MH 

36 

4 

0 

0 

6 

29 

5 

0 

11 

20 9 

0 

CB6PH 

31 

9 

0 

0 

32 

8 

0 

0 




CB7PH 

36 

4 

0 

0 

33 

5 

2 

0 




CB8PH* 

39 

1 

0 

0 








BSHOH* 

37 

0 

0 

1 








GUNOH** 

38 

0 

1 

1 








MIDOH* 

40 

0 

0 

0 








BACOH** 

36 

0 

0 

4 








PATMH 

40 

0 

0 

0 

0 

7 

33 

0 

1 

1 7 

0 

MAGMH- 

8 

16 

16 

0 








SEVMH- 

7 

9 

19 

4 








SOUMH** 

3 

2 

31 

3 








RHDMH** 

37 

0 

1 

1 








WSTMH** 

28 

3 

5 

3 








PAXTF* 

40 

0 

0 

0 








WBRTF* 

40 

0 

0 

0 








PAXOH** 

31 

0 

2 

7 








PAXMH 

25 

15 

0 

0 

8 

11 

21 

0 




POTTF* 

39 

1 

0 

0 








PISTF** 

38 

2 

0 

0 








MATTF* 

39 

1 

0 

0 








POTOH* 

39 

1 

0 

0 








POTMH 

39 

1 

0 

0 

5 

25 

10 

0 

10 

7 22 

0 

RPPTF* 

39 

0 

0 

0 








RPPOH* 

39 

0 

0 

0 








RPPMH 

35 

4 

1 

0 

24 

15 

1 

0 

22 

8 3 

0 

CRRMH** 

20 

2 

11 

7 








PIAMH** 

38 

2 

0 

0 








MPNTF 

29 

0 

0 

8 








MPNOH 

25 

0 

0 

13 








PIMKTF 

26 

0 

3 

10 








PMKOH 

22 

0 

0 

17 








YRKMH** 

30 

0 

2 

8 








YRKPH** 

35 

0 

0 

5 

32 

2 

3 

1 




MOBPH- 

25 

14 

1 

0 








JMSTF* 

40 

0 

0 

0 








APPTF* 

39 

0 

0 

0 








JMSOH* 

40 

0 

0 

0 








CFIKOH* 

40 

0 

0 

0 








JMSMH* 

40 

0 

0 

0 








JMSPH* 

39 

0 

0 

1 








WBEMH** 

31 

0 

1 

7 








SBEMH 

22 

0 

4 

13 

29 

0 

3 

2 




EBEMH 

25 

0 

2 

12 








LAFMH** 

17 

0 

0 

3 








ELIPH** 

36 

0 

3 

1 








NORTF* 

40 

0 

0 

0 






continued 

C&DOH* 

40 

0 

0 

0 









chapter v 


Guidance for Attainment Assessment of Instantaneous Minimum and 7-Day Mean Dissolved Oxygen Criteria 








Table V-8 (continued). Characterization of the Chesapeake Bay Program segments 

based on occupied quadrants in a plot of the 1 percent dis¬ 
solved oxygen concentration versus observed monthly mean 
dissolved oxygen concentration 1 . 


Number of Data Points By Quadrant by Designated Use 


CBP 

Segment 


Open- 

-Water 


1 

2 

3 

4 

BOHOH* 

39 

0 

0 

1 

ELKOH* 

39 

0 

0 

0 

SASOH* 

39 

0 

0 

1 

CHSOH* 

39 

0 

0 

1 

CHSMH 

37 

2 

1 

0 

EASMH 

39 

1 

0 

0 

CHOOH** 

34 

0 

0 

6 

CHOMH2** 

26 

2 

9 

3 

CHOMH1 ** 

33 

6 

1 

0 

LCHMH- 

4 

11 

24 

0 

FSBMH* 

36 

0 

0 

1 

NANTF** 

35 

0 

0 

5 

NANMH* 

38 

0 

0 

0 

WICMH 

28 

0 

0 

10 

MANMH* 

37 

0 

0 

1 

B1GMH* 

38 

0 

0 

0 

POCTF 

18 

0 

3 

19 

POCMH* 

40 

0 

0 

0 

TANMH** 

27 

6 

5 

1 


Deep-Water 

12 3 4 


12 8 14 1 

1 13 20 2 


Deep-Channel 

12 3 4 


2 0 3 0 

2 0 2 0 


'Quad 1: both 30-day mean and instantaneous minimum criteria achieved; quad 2: 30-day mean criterion 
achieved, instantaneous minimum criterion not achieved; quad 3: both 30-day mean and instantaneous minimum 
criteria not achieved; quad 4: 30-day mean criterion not achieved, instantaneous minimum criterion achieved. 
Based on data from the Chesapeake Bay Water Quality Monitoring Program twice monthly cruises between June 
and September, 1993 through 2002 (most recent 10 years). 

Single asterisk (*): Open-water use only segment with all data points in quadrant 1 and none or only one data 
point in the other three quadrants. 

Double asterisk (**): Open-water use only segment with a vast majority of data points (greater than two-thirds) 
in either quadrant 1 or quadrant 3. 

Single dash(-): Open-water use only segment with sufficient data points in quadrant 2 indicating a much higher 
occurrence where the 30-day mean criterion was achieved yet the instantaneous minimum criterion was not 
achieved. 


Boldface type: Open-water use only segment with a large number of data points in quadrant 1 and quadrant 4 and 
none or very few data points in the other two quadrants. 

Source: Chesapeake Bay Water Quality Monitoring Program database. 
http://www.chesapeakebay.net/data 


Guidance for Attainment Assessment of Instantaneous Minimum and 7-Day Mean Dissolved Oxygen Criteria 








Table V-9. Chesapeake Bay Program segments and tidal water designated uses where attainment of the instantaneous minimum, 1-day 
mean and 7-day mean dissolved oxygen criteria can be assessed using 30-day mean data or dissolved oxygen criteria 
attainment assessment may require collection and evaluation of data of higher frequency than 30-day means. 


59 


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CB20II 

CB3MH 

CB4MH 

CB5MH 

CB6PH 

CB7PH 

CB8PH 

BSHOH 

GUNOH 

MIDOH 

BACOH 

PATMH 

MAGMH 

SEVMH 

SOUMH 

RHDMH 

WSTMH 

PAXTF 

WBRTF 

PAXOH 

PAXMH 

POTTF 




























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Segment Name 

Northern Chesapeake Bay 

Upper Chesapeake Bay 

Upper Central Chesapeake Bay 

Middle Central Chesapeake Bay 

Lower Central Chesapeake Bay 

Western Lower Chesapeake Bay 

Eastern Lower Chesapeake Bay 

Mouth of the Chesapeake Bay 

Bush River 

Gunpowder River 

Middle River 

Back River 

Patapsco River 

Magothy River 

Severn River 

South River 

Rhode River 

West River 

Upper Patuxent River 

Western Branch Patuxent River 

Middle Patuxent River 

Lower Patuxent 

Upper Potomac River 


chapter v 


Guidance for Attainment Assessment of Instantaneous Minimum and 7-Day Mean Dissolved Oxygen Criteria 


continued 






































Table V-9 (continued). Chesapeake Bay Program segments and tidal water designated uses where attainment of the instantaneous min¬ 
imum, 1-day mean and 7-day mean dissolved oxygen criteria can be assessed using 30-day mean data or dis¬ 
solved oxygen criteria attainment assessment may require collection and evaluation of data of higher frequency 
than 30-day means. 


60 


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X 

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X 

X 

X 

X 

X 

X 

X 

X 

X 





X 

X 


X 

X 

X 

X 

X 

X 

Chesapeake Bay Program Segment 

Segment 

Code 

ANATF 

PISTF 

MATTF 

POTOH 

POTMH 

RPPTF 

RPPOH 

RPPMH 

CRRMH 

PIAMH 

MPNTF 

MPNOH 

PMKTF 

PMKOH 

YRKMH 

YRKPH 

MOBPH 

JMSTF 

APPTF 

JMSOH 

CHKOH 

JMSMH 

JMSPH 

Segment Name 

Anacostia River 

Piscataway Creek 

Mattawoman Creek 

Middle Potomac River 

Lower Potomac River 

Upper Rappahannock River 

Middle Rappahannock River 

Lower Rappahannock River 

Corrotoman River 

Piankatank River 

Upper Mattaponi River 

Lower Mattaponi River 

Upper Pamunkey River 

Lower Pamunkey River 

Middle York River 

Lower York River 

Mobjack Bay 

Upper James River 

Appomattox River 

Middle James River 

Chickahominy River 

Lower James River 

Mouth of the James River 


chapter v 


Guidance for Attainment Assessment of Instantaneous Minimum and 7-Day Mean Dissolved Oxygen Criteria 














































61 


i/l-day day 
riteria 
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Water 


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X 

















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= a> £ 

mm e 5/5 

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Water 


X 












X 










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Water 

X 



X 

X 

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X 

X 

X 

X 

X 

Q/N 

X 

X 

X 

N/D 

X 

X 

X 


N/D 

X 

X 

Chesapeake Bay Program Segment 

Segment 

Code 

WBEMH 

SBEMH 

EBEMH 

LAFMH 

ELIPH 

LYNPH 

NORTF 

C&DOH 

BOHOH 

ELKOH 

HOSVS 

CHSTF 

CHSOH 

CHSMH 

EASMH 

CHOTF 

CHOOH 

CHOMH2 

CHOMH1 

LCHMH 

HNGMH 

FSBMH 

NANTF 

Segment Name 

Western Branch Elizabeth River 

Southern Branch Elizabeth River 

Eastern Branch Elizabeth River 

Lafayette River 

Mouth to mid-Elizabeth River 

Lynnhaven River 

Northeast River 

C&D Canal 

Bohemia River 

Elk River 

Sassafras River 

Upper Chester River 

Middle Chester River 

Lower Chester River 

Eastern Bay 

Upper Choptank River 

Middle Choptank River 

Lower Choptank River 

Mouth of the Choptank River 

Little Choptank River 

Honga River 

Fishing Bay 

Upper Nanticoke River 


chapter v 


Guidance for Attainment Assessment of Instantaneous Minimum and 7-Day Mean Dissolved Oxygen Criteria 


continued 








































Table V-9 (continued). Chesapeake Bay Program segments and tidal water designated uses where attainment of the instantaneous min¬ 
imum, 1-day mean and 7-day mean dissolved oxygen criteria can be assessed using 30-day mean data or dis¬ 
solved oxygen criteria attainment assessment may require collection and evaluation of data of higher frequency 
than 30-day means. 



3 

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3 

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3 

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3 

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nt may requii 
data than 30 

Deep- 

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it 

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3 

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3 

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C 

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assessme 

frequency 

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Water 



X 



X 




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X 

X 


N/D 

X 

X 


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it 

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WD 

it 

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Segment 

Code 

NANOH 

NANMH 

WICMH 

MANMH 

BIGMH 

POCTF 

POCOH 

POCMH 

TANMH 













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Segment Name 

Middle Nanticoke River 

Lower Nanticoke 

Wicomico River 

Manokin River 

Big Annemessex River 

Upper Pocomoke River 

Middle Pocomoke River 

Lower Pocomoke Sound 

Tangier Sound 


JO 

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chapter v 


Guidance for Attainment Assessment of Instantaneous Minimum and 7-Day Mean Dissolved Oxygen Criteria 


























63 


assessing attainment of 30-day mean and instantaneous minimum dissolved oxygen 
criteria within these five segments are cautioned to not automatically assume attain¬ 
ment of the 30-day mean criterion reflects attainment of the instantaneous minimum 
criterion (Table V-9). Site-specific buoy deployments may be necessary to either 
better quantify a relationship or assess attainment using both low- and high- 
frequency data sources. 

Seven segments with only open-water designated uses had a large number of data 
points in quadrant 1 (both criteria were achieved) and in quadrant 4 (instantaneous 
minimum criterion achieved, but the 30-day mean criterion not achieved) and none 
or very few data points in other quadrants were marked in bold typeface in Table V- 
8. These seven segments were: upper (MPNTF) and lower (MPNOH) Mattaponi, 
upper (PMKTF) and lower (PMKOH) Pamunkey River, Eastern Branch Elizabeth 
River (EBEMH), Wicomico River (WICMH), and upper Pocomoke River (POCTF.) 

The segments in the Pamunkey and Mattaponi rivers (segments PMKTF, PMKOH 
and MPNTF, MPNOH, respectively) are known to be strongly influenced by rela¬ 
tively large expanses of fringing wetlands along the entire length of both tidal rivers. 
The Wicomico River (WICMH) and upper Pocomoke River (POCTF) also have 
large areas of tidal wetlands along particular reaches of these two rivers. The natural 
influences of extensive fringing tidal wetlands systems, described in more detail in 
Chapter 6, are the likely reason for why the 30-day mean/instantaneous minimum 
relationship does not fully apply to these seven segments. More site specific evalua¬ 
tion of the data and conditions within the Eastern Branch of the Elizabeth River 
(EBEMH) is required to understand what’s happening in this tidal system. 

Users assessing attainment of the 30-day mean and instantaneous minimum 
dissolved oxygen criteria within these seven segments are cautioned not to automat¬ 
ically assume that attainment of the 30-day mean criterion reflects attainment of the 
instantaneous minimum criterion (Table V-9). Site-specific buoy deployments may 
be necessary either to better quantify a relationship or assess attainment using both 
low- and high-frequency data sources. 

For the remaining seven segments with only open-water designated uses, there were 
insufficient buoy data available to assess whether attainment of the 30-day mean 
criterion reflected attainment of the instantaneous minimum criterion. These 
segments are marked with a “N/D” in Table V-9. 

Of the thirteen segments with deep-water or deep-water and deep-channel desig¬ 
nated uses, eleven of the segments had the vast majority (greater than two-thirds) of 
their open-water designated use data points in quadrant 1 (Table V-8), directly 
supporting the assessment of attainment of the instantaneous minimum criterion 
directly based on assessment of attainment of the 30-day mean criterion in these 
segments (Table V-9). Users assessing attainment of the 30-day mean and instanta¬ 
neous minimum dissolved oxygen criteria within the lower Patuxent River 
(PAXMH) and Southern Branch Elizabeth River (SBEMH) are cautioned not to 
automatically assume that attainment of the 30-day mean criterion reflects attain¬ 
ment of the instantaneous minimum criterion. 


chapter v 


Guidance for Attainment Assessment of instantaneous Minimum and 7-Day Mean Dissolved Oxygen Criteria 


64 


Ten of these thirteen segments with deep-water or deep-water and deep-channel 
designated uses also showed evidence of a strong relationship between achieved/not 
achieved in the assessment of the instantaneous minimum using monthly mean data 
for the deep-water and/or deep channel designated uses (Table V-8). These segments 
were: middle central Chesapeake Bay (CB4MH), western lower Chesapeake Bay 
(CB6PH), eastern lower Chesapeake Bay (CB7PH), Patapsco River (PATMH), lower 
Potomac River (POTMH) [deep-channel use only], lower Rappahannock River 
(RPPMH) [deep-channel use only], lower York River (YRKPH), Southern Branch 
Elizabeth River (SBEMH), lower Chester River (CSHMH), and Eastern Bay 
(EASMH) [deep channel use only] (Table V-9). 

In the cases of the upper central Chesapeake Bay (CB3MH), lower central Chesa¬ 
peake Bay (CB5MH), lower Patuxent River (PAXMH), lower Potomac River 
(POTMH) [deep-water use only], lower Rappahannock River (RPPMH) [deep-water 
use only] and Eastern Bay (EASMH) [deep-water use only] there are sufficient data 
points in quadrant 2 indicating a higher occurrence where the 30-day mean criteria 
were achieved yet the instantaneous minimum criteria were not achieved in deep¬ 
water and/or deep-channel designated use habitats (Table V-8). Users assessing 
attainment of 30-day mean and instantaneous minimum dissolved oxygen criteria 
within these seven segments and their respective deep-water/deep channel desig¬ 
nated uses are cautioned not to automatically assume that attainment of the 30-day 
mean criterion reflects attainment of the instantaneous minimum dissolved oxygen 
criterion (Table V-9). Site-specific buoy deployments may be necessary either to 
better quantity a relationship or assess attainment using both low- and high- 
frequency data sources. 


ASSESSMENT OF 7-DAY MEAN CRITERIA ATTAINMENT 

FROM MONTHLY MEAN DATA 

The open-water designated use habitats are also subject to a 7-day mean criterion. 

The continuous buoy data were examined to look for relationships between the 30- 
day mean and the 7-day mean values. Buoy data records with durations over 14 days 
(at least two 7-day periods) were examined. Figure V-4 shows plots of the sequen¬ 
tial as opposed to a rolling series of 7-day means versus the 30-day mean for the 
more limited number of data records that were available. There is more scatter in 
these relationships than in the 30-day mean versus instantaneous minimum relation¬ 
ships. However, a significant majority of the data points are found in the first and 
third quadrants, where the data points both achieve (quadrant 1) or both do not 
achieve (quadrant 3) the 30-day mean and 7-day mean criteria. There is clearly a 
strong relationship between achieving/not achieving of the 30-day mean and 7-day 
mean criteria. The remaining data points tended to be in the second quadrant where 
the data points do not achieve the 30-day mean criterion but achieve the 7-day mean 
criterion. Only 3 data points were located in the fourth quadrant. 

chapter v • Guidance for Attainment Assessment of Instantaneous Minimum and 7-Day Mean Dissolved Oxygen Criteria 





65 


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Monthly Mean Dissolved Oxygen Concentration 


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Monthly Mean Dissolved Oxygen Concentration 


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0 2 4 6 8 10 12 

Monthly Mean Dissolved Oxygen Concentration 


PAXMH Open—Water 



Monthly Mean Dissolved Oxygen Concentration 


Figure V-4. Plots of monthly mean dissolved oxygen concentration (mg liter 1 ) versus the 7-day mean dissolved 
oxygen concentration (mg liter 1 ) in several example Chesapeake Bay Program segments: open-water and deep¬ 
water middle central Chesapeake Bay (CB4MH), Mobjack Bay (MOBPH), lower Choptank River (CHOMH1), middle 
Potomac River (POTOH) and lower Patuxent River (PAXMH). 

Source: Chesapeake Bay Water Quality Monitoring Program database. 
http://www.chesapeakebay.net/data 


chapter v 


Guidance for Attainment Assessment of Instantaneous Minimum and 7-Day Mean Dissolved Oxygen Criteria 












































66 


FINDINGS 

For the majority of Chesapeake Bay Program segments and the designated use habi¬ 
tats within those segments identified in Table V-9, dissolved oxygen concentration 
data collected through monthly to twice monthly sampling at the Chesapeake Bay 
Water Quality Monitoring Program fixed-stations can be used to assess attainment 
of all higher frequency dissolved oxygen criteria components including the 7-day 
mean, 1-day mean and instantaneous minimum criteria. For the remaining segments 
and identified designated uses, further targeted buoys deployments are required to 
more fully characterize and quantify the relationships between the monthly mean, 7- 
day mean, 1-day mean and instantaneous minimum concentrations. Further work is 
underway to factor in additional variables to strengthen the predictive relationships 
between the 30-day mean, 7-day mean, 1-day mean and instantaneous minimum 
values and therefore, the assessment of attainment of the instantaneous minimum, 1- 
day mean and 7-day mean criteria using monthly mean observations. 


LITERATURE CITED 

Jordan, S.J., C. Stenger, M. Olson, R. Batiuk and K. Mountford. 1992. Chesapeake Bay 
Dissolved Oxygen Goal for Restoration of Living Resource Habitats: A Synthesis of Living 
Resource Requirements with Guidelines for Their Use in Evaluating Model Results and 
Monitoring Information. CBP/TRS 88/93. Region III Chesapeake Bay Program Office, 
Annapolis, Maryland. 

U.S. Environmental Protection Agency. 2003. Ambient Water Quality • Criteria for Dissolved 
Oxygen. Water Clarity' and Chlorophyll a for the Chesapeake Bay and Its Tidal Tributaries. 
EPA 903-R-03-002. Region III Chesapeake Bay Program Office, Annapolis, Maryland. 


chapter v 


Guidance for Attainment Assessment of Instantaneous Minimum and 7-Day Mean Dissolved Oxygen Criteria 







chapter \/i 


Guidance for Deriving Site 
Specific Dissolved Oxygen 
Criteria for Assessing Criteria 
Attainment of Naturally Low 
Dissolved Oxygen 
Concentrations in Tidal Wetland 
Influenced Estuarine Systems 


Tidal wetlands are a valuable component of estuarine systems. In the Pamunkey 
River, they have been shown to be net sinks for sediments (Neubauer et al. 2001) and 
in most cases also serve to remove nutrients from overlying water (Anderson et al. 
1997). High rates of organic production, accompanied by high rates of respiration 
(Neubauer et al. 2000), can significantly reduce dissolved oxygen and enhance 
dissolved inorganic carbon levels both in sediment pore water and overlying water 
in wetland systems. Another process that can deplete dissolved oxygen in wetland 
sediments is nitrification, which converts ammonium to nitrite and nitrate (Tobias et 
al. 2001). 

Subsequent to publication of Ambient Water Quality' for Dissolved Oxygen, Water 
Clarity and Chlorophyll a for the Chesapeake Bay and Its Tidal Tributaries (U.S. 
EPA 2003a), Virginia, Maryland, Delaware and the District of Columbia initiated 
their respective processes for adopting new and/or revising existing state water 
quality standards. In so doing, Virginia requested support and guidance from EPA in 
determining the appropriate dissolved oxygen criteria/designated use/attainment 
procedures for the tidal Mattaponi and Pamunkey rivers for addressing the naturally 
lower ambient dissolved oxygen concentrations. Based on the scientific literature 
and personal communications with Chesapeake Bay wetland scientists, EPA recog¬ 
nized the need to explore accommodations for the special circumstances in these 
tidal wetland influenced estuarine systems with respect to criteria levels, designated 
uses and/or criteria attainment assessment. 


chapter vi 


Guidance for Deriving Site Specific Dissolved Oxygen Criteria 


NATURAL CONDITIONS/FEATURES INDICATING 
ROLE OF WETLANDS IN LOW DISSOLVED 
OXYGEN CONCENTRATIONS 

A future objective is to define more fully the natural conditions and physical features 
in Chesapeake Bay tidal systems that would indicate that tidal wetlands are playing 
a significant role in naturally reducing ambient dissolved oxygen concentrations. 
Those natural conditions/features have not yet been firmly established but Tables 
VI-1 and VI-2 provide some key physical and water quality statistics for the tidal 
Mattaponi and Pamunkey rivers. Appendix A provides similar data for other tidal 
fresh and oligohaline regions in the Chesapeake Bay and its tidal tributaries for 
comparison. Four natural conditions/features have been evaluated here to document 
and help quantify the influence of tidal wetlands on the dissolved oxygen deficit 
observed in the tidal Mattaponi and Pamunkey rivers. 

SURFACE TO VOLUME RATIOS/LARGE FRINGING WETLAND AREAS 

The tidal fresh and oligohaline segments in the Mattaponi and Pamunkey rivers are 
among the smallest volume, with a small surface to volume ratio and large areas of 
fringing tidal marsh—1.5 times larger than the tidal surface water area—relative to 
other segments throughout the Bay’s tidal waters (Table VI-1; Appendix A, Table A-l). 

WATER QUALITY CONDITIONS 

Table VI-2 gives some water quality statistics for recent years. These years happen 
to have had dry to record-dry summers and that low flow regime should be borne in 
mind. Severe low dissolved oxygen conditions (concentrations < 3 mg liter 1 ) are not 
obvious, but average dissolved oxygen concentrations, in both surface and bottom 
waters, are about 2.5 to 3 mg liter' 1 below calculated oxygen saturation levels (Table 
VI-2). Chlorophyll a concentrations are comparatively low, as are the total nitrogen 
concentrations (with the exception of the oligohaline Pamunkey River segment 
PMKOH). Phosphorus concentrations range from mid to high compared to other 
tidal systems. 

The dissolved oxygen deficit in these two tidal systems is among the highest 
observed in the Chesapeake Bay’s tidal tributaries. The dissolved oxygen deficits 
observed in the recent dry years (Table VI-2) are similar to those observed over the 
1985-2002 Chesapeake Bay water quality monitoring program data record (Figure 
VI-1). These findings indicate that the processes driving the recorded dissolved 
oxygen deficits are due largely to natural processes internal to the tidal system and 
not as much to external nonpoint nutrient loadings (which are naturally reduced 
during the recent dry years due to decreased surface runoff). 


chapter vi 


Guidance for Deriving Site Specific Dissolved Oxygen Criteria 




69 


Table VI-1 . Some physical characteristics of the Mattaponi and Pamunkey tidal fresh (MPNTF and TMKTF, 
respectively) and oligohaline (MPNOH and PMKOH, respectively) segments: depth distribution 
based on depth of cells in the Chesapeake Bay Program volumetric interpolator, acres of fringing 
tidal wetlands, segment perimeter, segment water surface area, segment water column volume 
and segment water surface area:water column volume ratio. 


Maximum 
CBP Depth 

Segment (meters) 

75th 

Percentile 

(meters) 

Median 

Depth 

(meters) 

25th 

Percentile 

(meters) 

Minimum 

Depth 

(meters) 

Wetland 

Acreage 

(acres) 

Segment 

Perimeter 

(meters) 

Segment 
Surface Area 
(meters 2 ) 

Segment 

Volume 

(meters 3 ) 

Surface Area 
to Volume 
Ratio 

MPNTF 

12 

3 

2 

1 

1 

1,125 

108,327 

8,573,187 

15,337,500 

0.6 

MPNOH 

15 

5 

3 

2 

1 

3,360 

109,059 

8,660,891 

35,390,000 

0.2 

PMKTF 

15 

4 

2 

1 

1 

1,652 

264,699 

16,229,024 

28,630,000 

0.6 

PMKOH 

18 

5 

3 

2 

1 

5,374 

119,417 

14,093,807 

66,680,000 

0.2 

Source: Chesapeake Bay Program http://ww\ 

v.chesapeakebay.net/data 







Table VI-2. Recent summer averaged water quality conditions in the Mattaponi and Pamunkey tidal fresh 

(MPNTF and PMKTF, respectively) and oligohaline (MPNOH and PMKOH, respectively) segments for 
2000-2002, dry to record dry summers. 

CBP 

Segment 

Water 
Water Column 

Column Depth 

Layer (meters) 

Salinity 

(PPO 

Temperature 

(°C) 

Dissolved 
Oxygen 
Concentration 
(mg liter 1 ) 

Dissolved 
Oxygen 
Deficit 
(mg liter' 1 ) 

Chlorophyll a 
Concentration 
(ug liter 1 ) 

Total 

Suspended 

Solids 

Concentration 
(mg liter 1 ) 

Total Total 

Nitrogen Phosphorus 

Concentration Concentration 
(mg liter 1 ) (mg liter 1 ) 

MPNTF 

S 0.7 

0.0 

27.3 

5.6 

2.4 

5.9 

10.3 

0.61 

0.079 

MPNTF 

B 3.0 

0.0 

27.2 

5.6 

2.4 

• 

12.3 

0.61 

0.080 

MPNOH 

S 0.7 

7.4 

26.8 

5.6 

2.1 

10.6 

35.4 

0.76 

0.115 

MPNOH 

B 14.3 

8.4 

26.5 

5.0 

2.7 


100.6 

0.94 

0.174 

PMKTF 

S 0.7 

0.3 

26.9 

5.3 

2.5 

6.2 

18.3 

0.61 

0.084 

PMKTF 

B 6.1 

0.3 

26.8 

5.5 

2.6 


31.0 

0.68 

0.107 

PMKOH 

S 0.7 

6.6 

26.2 

5.0 

2.9 

12.6 

46.0 

0.73 

0.105 

PMKOH 

B 5.2 

7.0 

26.2 

4.9 

3.0 


139.9 

1.11 

0.220 


S = surface 
B = bottom 

Source: Chesapeake Bay Water Quality Monitoring Program database, http: www.chesapeakebay.net data 


chapter vi 


Guidance for Deriving Site Specific Dissolved Oxygen Criteria 






70 


MPNTF Surface 


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Figure VI-1. Time series plots of ambient dissolved oxygen concentrations (mg liter 1 ) and calculated dissolved 
oxygen saturation concentrations (mg liter 1 ) and resultant calculated dissolved oxygen deficit (saturation 
concentration minus ambient concentration) in surface and bottom waters of the tidal fresh segments of the 
Mattaponi (MPNTF) and Pamunkey (PMKTF) rivers. 


Source: Chesapeake Bay Water Quality Monitoring Program database, http://www.chesapeakebay.net/data 


chapter vi 


Guidance for Deriving Site Specific Dissolved Oxygen Criteria 





















































71 


DISSOLVED OXYGEN/TEMPERATURE RELATIONSHIPS 

Another natural feature of tidal systems strongly influenced by extensive adjacent 
tidal wetlands would be a strong relationship between the ambient dissolved oxygen 
concentrations (and dissolved oxygen deficit) and water temperature, useful for 
separating out the wetlands’ effect on dissolved oxygen versus an anthropogenic 
effect. Figure VI-2 shows dissolved oxygen concentration and dissolved oxygen 
deficit plotted versus water temperature for the tidal fresh and oligohaline segments 
of the Mattaponi and Pamunkey rivers and for the tidal fresh and oligohaline 
segments of the Rappahannock and Patuxent rivers for comparison. All the plots 
illustrated in Figure VI-2 show dissolved oxygen concentrations going down as 
water temperature rises due to decreasing saturation concentrations and likely 
increased biological/chemical demand. 

In the Rappahannock and Patuxent segments, however, dissolved oxygen concentra¬ 
tions begin to trend back upward (and the dissolved oxygen deficit levels out) as 
temperatures continue to increase. Presumably the generation of oxygen from plank¬ 
tonic algal photosynthesis at these increasing temperatures provides the beneficial 
boost during the daytime when these measurements were collected. 

This trend effect in which dissolved oxygen concentrations increase as temperatures 
continue to increase is not evident in the Mattaponi and Pamunkey segments. Based 
on a comparison of the values in Table VI-2 and Appendix A, the difference in 
chlorophyll a concentrations in Rappahannock and Patuxent (higher concentrations) 
versus Mattaponi and Pamunkey river segments (lower concentrations) supports this 
hypothesis. These findings lend further evidence of the lack of a strong influence of 
planktonic algal photosynthesis on dissolved oxygen concentrations with the 
Mattaponi and Pamunkey rivers. 

LOW VARIABILITY IN DISSOLVED OXYGEN CONCENTRATIONS 

One could also hypothesize that, within the temperature trend described above and 
illustrated in Figure VI-2, there should be less scatter in the data points in a system 
whose ‘stressor’ exerted its effect in a relatively constant manner, as the wetlands 
might. While this hypothesis may be true and is suggested in the plots provided in 
Figure VI-2, the differences among the segments in the number and diversity of 
stations contributing data points is confounding a clearer conclusion. Table VI-3, 
however, provides further quantitative information on dissolved oxygen concentra¬ 
tion variability in the Mattaponi and Pamunkey segments which does support that 
hypothesis. 

Through the long-term Chesapeake Bay Water Quality Monitoring Program, 
Virginia has been collecting monthly or twice monthly dissolved oxygen measure¬ 
ments (surface and bottom) at fixed stations in the Mattaponi and Pamunkey tidal 
fresh and oligohaline segments since 1985. The data are collected in the daytime and 
each measurement represents one point in time in the month or two-week interval. 


chapter v 


Guidance for Deriving Site Specific Dissolved Oxygen Criteria 


72 


MPNTF Surface 


MPNOH Surface 



Water Temperature 


Water Temperature 


PMKTF Surface 


PMKOH Surface 



Water Temperature 


Water Temperature 


RPPTF Surface 


RPPOH Surface 



Water Temperature 


Water Temperature 


PAXTF Surface 


PAXOH Surface 



Water Temperature 


Water Temperature 


Figure VI-2. Plots of measured ambient dissolved oxygen concentrations (•, mg liter 1 ) and calculated dissolved 
oxygen deficit (o, mg liter 1 ) versus water temperature (°C) in tidal fresh and oligohaline segments of the Mattaponi 
(MPNTF and MPNOH, respectively) and Pamunkey (PMKTF and PMKOH, respectively) rivers and in the tidal fresh 
and oligohaline segments of Rappahannock (RPPTF and RPPOH, respectively) and Patuxent (PAXTF and PAXOH, 
respectively) rivers for comparison. 

Source: Chesapeake Bay Water Quality Monitoring Program database, http://www.chesapeakebay.net/data 


chapter vi 


Guidance for Deriving Site Specific Dissolved Oxygen Criteria 
























































73 


In 2003, in-situ, continuous monitoring devices were deployed by the Virginia Insti¬ 
tute of Marine Science at a number of sites within both tidal rivers and all four 
salinity-based segments. These ‘buoys’ were deployed to collect data at time-scales 
more relevant to the Chesapeake Bay dissolved oxygen criteria, which have 7-day 
mean and instantaneous minimum as well as the 30-day mean averaging periods 
(U.S. EPA 2003a). These buoys collect dissolved oxygen concentration and other 
physical data continuously at 15-minute intervals. 

For the comparisons in Table VI-3, the mean and other statistics of the long-term 
daytime Chesapeake Bay Water Quality Monitoring Program measurements were 
computed for each month over the 18-year record, separately for surface (water 
column depth = 1 meter) and bottom (where the water column depth was >1 meter) 
waters. The continuous buoy data were divided into day (6:00 AM-5:59 PM) and 
night (6:00 PM-5:59 AM) periods. All the buoys were deployed at the fixed depths 
listed in Table VI-3. 

The low variability in dissolved oxygen concentrations measured in the Mattaponi 
and Pamunkey segments are documented by four separate measures: 1) the small 
within-month range of concentrations measured in the Chesapeake Bay Water 
Quality Monitoring Program over the 18-year data record; 2) the small dissolved 
oxygen concentration differences between surface and deeper waters (long-term 
water quality monitoring program data station); 3) the good agreement between 
dissolved oxygen concentrations measured at the long-term water quality monitoring 
program stations and the continuous buoy sites; and 4) the small differences between 
day and night concentrations recorded in the continuous buoy data. Similar compar¬ 
isons are becoming possible in other Chesapeake Bay and tidal tributary segments 
with expanded implementation of shallow water and continuous buoy deployment 
monitoring programs. This expanding data record will be evaluated in the future to 
further confirm low-variability in dissolved oxygen concentrations are an important 
characteristic of segments where extensive tidal wetlands are directly influencing 
ambient dissolved oxygen concentrations. 


APPROACHES FOR ADDRESSING NATURALLY 
LOW DISSOLVED OXYGEN CONDITIONS 
DUE TO TIDAL WETLANDS 

Four approaches for addressing naturally low ambient dissolved oxygen concentra¬ 
tions due to adjacent extensive tidal wetlands within the context of state water 
quality standards were considered: 

1. Define a completely new designated use with the appropriate dissolved oxygen 
criteria. 

2. Develop a separate biological reference curve that would account for lower 
dissolved oxygen values in wetland-dominated tidal water segments. 


chapter vi 


Guidance for Deriving Site Specific Dissolved Oxygen Criteria 




74 


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chapter vi 


Guidance for Deriving Site Specific Dissolved Oxygen Criteria 







76 


3. Determine a fixed or multivariate compensation factor to ‘adjust’ (upward) the 
observed dissolved oxygen concentration values. The adjusted values would be 
substituted for observed values in the criteria attainment assessment protocol used 
for all affected designated uses, i.e., comparing the cumulative frequency distri¬ 
bution curve of observed values to the biological reference curve. 

4. Derive a set of site-specific dissolved oxygen criteria values that factor in the 
natural dissolved oxygen deficit. 

The first approach—a completely new designated use—was rejected because the 
species and habitat requirements of those species that should be protected in these 
tidal wetland dominated segments are the same species that occupy other open-water 
designated use tidal water segments of similar salinity regimes. The assumption is 
that in these areas, the species’ dissolved oxygen requirements are the same but that 
they may modify their behavior, utilize the area differently or otherwise make 
accommodation for the natural effect of the tidal wetlands on ambient dissolved 
oxygen concentrations with some level of adverse effects. 

The second approach—developing a separate biological reference curve—was 
rejected because the biological reference levels are, by definition, based on ambient 
dissolved oxygen conditions exhibited by areas supporting high functioning living 
resources. Even if this definition were abandoned in favor of a curve or curves based 
on specific natural impairments, then the Mattaponi and Pamunkey segments would 
have to serve as their own reference sites since there are no other comparable 
segments within the Chesapeake Bay system. Taking this approach to deriving 
biological reference curves was difficult to rationalize. 

The third approach—to find an appropriate adjustment factor for observed concen¬ 
trations—was rejected because of concerns that the criteria, not the attainment 
procedures, should directly reflect the natural dissolved oxygen deficits caused by 
extensive tidal wetlands. 

The fourth option—derive a set of set specific dissolved oxygen criteria values—was 
recommended as the best approach to factor in the natural wetlands-caused dissolved 
oxygen deficit directly for the reasons and technical basis documented below. 


DERIVATION OF SITE-SPECIFIC DISSOLVED OXYGEN 
CRITERIA FACTORING IN NATURAL WETLAND-CAUSED 
DISSOLVED OXYGEN DEFICITS 

Through evaluation of three independent sources of information—scientific findings 
published in the peer reviewed literature, Chesapeake Bay water quality model simu¬ 
lations, and the long-term Chesapeake Bay Water Quality Monitoring Program data 
record—efforts were made to quantify the deficit in dissolved oxygen concentrations 
below oxygen saturation levels due to natural tidal wetland processes. Once 
quantified, the wetland-caused oxygen deficits could then be subtracted from 


chapter vi 


Guidance for Deriving Site Specific Dissolved Oxygen Criteria 













calculated oxygen saturation concentrations to determine the natural background 
oxygen levels that could be sustained within these wetland dominated tidal rivers 
absent any external anthropogenic nutrient pollutant loadings. 

SCIENTIFIC RESEARCH-BASED ESTIMATES OF 
WETLAND RESPIRATION 

As part of the analysis to examine dissolved oxygen criteria attainment in the various 
tidal wetland dominated segments, the Chesapeake Bay Water Quality Model was 
calibrated to account for wetland oxygen demand by applying a universal sediment 
oxygen demand of 2 grams 0 2 /meter 2 -day to all Chesapeake Bay tidal wetland areas. 
This value is a best professional judgement based on values published in the scien¬ 
tific literature and communication with Chesapeake Bay wetland scientists 
(Neubauer 2003). The scientific literature indicates wetland sediment oxygen 
demand in Northeastern United States ranges from 1 to 5.3 grams 0 2 /meter 2 -day 
(Neubauer et al. 2000; Cai et al. 1999). 

The value for sediment oxygen demand used in the previous 1998 Chesapeake Bay 
water quality model calibration (2 grams 0 2 /meter 2 -day) was re-examined and deter¬ 
mined to be accurate for the Mattaponi and Pamunkey rivers. Scott Neubauer of the 
Smithsonian Environmental Research Center (personal communication June 19, 
2003) estimates the marsh sediment oxygen consumption for Sweet Hall marsh, a 
freshwater marsh in the Pamunkey River, to range between 0.99-2.59 grams 
0 2 /meter 2 -day. Neubauer’s estimated ranges further support the sediment oxygen 
demand of 2 grams 0 2 /meter 2 -day that was used in the previous model calibration. 
Neubauer also concurred that the Mattaponi and Pamunkey systems are very similar 
(Neubauer 2003). Therefore, there was no need to recalibrate the sediment oxygen 
demand for either tidal tributary. 

MODEL-BASED WETLAND-CAUSED OXYGEN DEFICITS 

The impact of wetland oxygen demand on ambient dissolved oxygen concentrations 
was quantified for both the Mattaponi and Pamunkey segments through application 
of the Chesapeake Bay water quality model. A series of water quality model 
scenarios ‘with wetlands’ and ‘without wetlands’ were run to estimate the difference 
in model-adjusted interpolated monthly averaged dissolved oxygen concentration in 
the Mattaponi and Pamunkey segments. In the ‘with wetlands’ scenario, the water 
quality model simulated the full influence of the extensive adjacent tidal wetlands on 
ambient water quality conditions. In the ‘without wetlands' scenario, the tidal 
wetland functions of the model were turned off in the Mattaponi and Pamunkey 
model cells in order to simulate ambient water quality conditions in the absence of 
any influence by tidal wetlands. The summer monthly averaged dissolved oxygen 
concentration difference simulated by the ‘with wetlands’ scenario minus the 
‘without wetlands’ scenario was 3 mg liter” 1 , i.e., the open-water dissolved oxygen 
concentrations in the Mattaponi and Pamunkey segments with the presence of the 


chapter vi 


Guidance for Deriving Site Specific Dissolved Oxygen Criteria 


78 


extensive tidal wetlands were simulated to be 3 mg liter 1 lower than model esti¬ 
mated dissolved oxygen saturated concentrations. The model estimated 3 mg liter" 1 
oxygen deficit is fully consistent with the average dissolved oxygen deficits 
observed in monitoring data collected in these segments (see text below, Tables VI- 
2 and VI-3, Figure VI-1). 

MONITORING-BASED ESTIMATES OF WETLAND-CAUSED 
OXYGEN DEFICITS 

The dissolved oxygen concentration and oxygen saturation levels were calculated 
from the 1985-2002 Chesapeake Bay Water Quality Monitoring Program data 
collected at stations in the Mattaponi and Pamunkey segments. Over the 18-year data 
record, these stations were sampled at least monthly — sometimes twice monthly — 
as part of the long-term water quality monitoring program. The almost two-decade 
data record covers years of varying climatic and hydrologic conditions in the water¬ 
shed. Continuous, high frequency dissolved oxygen concentration data were also 
available for these segments, as described previously, but in most cases the duration 
of the data records is less than one year. Based on findings presented above, 
dissolved oxygen conditions characterized by the data collected at long-term (day¬ 
time) monitoring stations were very similar to those revealed by the continuous 
dissolved oxygen recording devices: short-term temporal and spatial variations in 
dissolved oxygen concentrations were relatively small; and deep nocturnal dips in 
dissolved oxygen concentrations were not observed in these segments. 

For this analysis, the long-term water quality monitoring data were partitioned into 
surface and bottom depths and into ‘cold’ (sampling events when water column 
temperatures were less than or equal to 15° C) and ‘warm’ (greater than 15° C) 
temperature categories. Table VI-4 shows: the calculated mean dissolved oxygen 
saturation concentration over the 18 year data record; the difference between calcu¬ 
lated oxygen saturation and actual observed dissolved oxygen concentrations, i.e., 
the dissolved oxygen deficit; the number and percent of dissolved oxygen measure¬ 
ments below the 5 mg liter 1 30-day mean criterion and below a 4 mg liter" 1 
concentration value; and the average magnitude of those episodic excursions below 
the 5 and 4 mg liter 1 values. Dissolved oxygen concentrations are always well above 
the 5 mg liter 1 30-day mean criterion in the cold months in the Mattaponi and 
Pamunkey river segments, so the cold month statistics are not discussed further. 

As presented earlier and previewed in Table VI-2, the average dissolved oxygen 
deficit in the warm (>15° C) months was 2.6 +/- 0.8 mg liter” 1 (Table VI-4). This 
long-term average monitoring data-based oxygen deficit value overlaps with the 
oxygen deficit of 3 mg liter" 1 estimated through the Bay water quality model simu¬ 
lation of tidal dissolved oxygen concentrations with and without tidal wetlands. 

The calculated dissolved oxygen saturation concentration in the Mattaponi and 
Pamunkey segments in the warm months was 8.5 +/- 0.7 mg liter" 1 . That means that, 
in the absence of any anthropogenic pollutant influences on water quality conditions, 


chapter vi 


Guidance for Deriving Site Specific Dissolved Oxygen Criteria 






79 


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81 


much of the time the fully saturated ambient dissolved oxygen concentrations would 
still above the 5 mg liter 1 30-day mean criterion level. However, from 13 to greater 
than 30 percent of the warm months’ monitoring-based observations fell below a 
monthly mean of 5 mg liter 1 with the magnitudes of these exceedences up to 0.7 mg 
liter 1 . These observations indicate that the segments would likely fail a summer¬ 
time application of the 5 mg liter 1 30-day mean criteria. Tested against a monthly 
mean concentration of 4 mg liter however, the percentage of observations falling 
below this concentration is less than 7 percent in most cases, and the magnitude of 
the exceedance is ~0.5 mg liter 1 (Table VI-4). 

The warm months calculated dissolved oxygen saturation concentration of 8.5 
+/-0.7 mg liter 1 directly translates into a dissolved oxygen concentration range of 
7.8 to 10.2 mg liter -1 . Similarly, the warm months average oxygen deficit of 2.6 
+/-0.8 mg liter 1 converts into a oxygen deficit concentration range of 1.6 to 3.4 mg 
liter -1 . Assuming a maximum long-term average oxygen deficit of 3.4 mg liter -1 , we 
could anticipate an ambient dissolved oxygen range of 6.8 to 4.4 mg liter -1 upon 
factoring in the oxygen deficit to a saturated water column condition. These are the 
best dissolved oxygen conditions, assuming the maximum oxygen deficit, one could 
ever hope to measure in the absence of any anthropogenic nutrient pollutant loading 
influence on ambient dissolved oxygen conditions. Even without any human 
impacts, the 5 mg liter 1 30-day mean dissolved oxygen criterion would be not 
attained all times in the warm months of the year, setting up the basis for a site- 
specific criterion based on natural conditions preventing attainment of the use (U.S. 
EPA 2003b). 

SITE-SPECIFIC DISSOLVED OXYGEN CRITERIA DERIVATION 

Factoring a natural tidal wetlands-based oxygen deficit into the oxygen saturation 
levels, based on the 18-year data record (see above), along with recognition that the 
antropogenic pollutant loads can be reduced but not eliminated (U.S. EPA 2003b), a 
site specific 4 mg liter -1 30-day mean criterion is recommended in place of the 
published 5 mg liter -1 30-day mean and 4 mg liter 1 7-day mean open-water desig¬ 
nated use criteria. The EPA-published 3.2 mg liter -1 instantaneous minimum 
dissolved oxygen criterion still applies to these waters year round (U.S. EPA 2003a). 
The 4 mg liter 1 30-day mean site-specific criterion applies only to the tidal fresh and 
oligohaline segments of the Mattaponi and Pamunkey rivers during the time period 
of June 1 through September 30. Outside of this time period, the EPA-published set 
of open-water designated use dissolved oxygen criteria apply (U.S. EPA 2003a). The 
water column temperatures during the October through May time-frame are such 
that higher levels of oxygen saturation are maintained and the biological processes 
driving the natural tidal wetland oxygen deficits do not have nearly the same level of 
influence on ambient dissolved oxygen concentrations. 

This approach assumes that the nature of the wetland effect on dissolved oxygen is 
relatively constant within season and that there are no other major stresses on 


chapter vi 


Guidance for Deriving Site Specific Dissolved Oxygen Criteria 



82 


dissolved oxygen in the system as documented previously. This results in relatively 
stable dissolved oxygen concentrations, which although sometimes below the 5 mg 
liter 1 30-day mean criterion level due to natural oxygen deficits, remain substantially 
above the instantaneous minimum criterion. The magnitude of the wetland-caused 
oxygen deficit is not enough to cause the calculated oxygen saturated concentrations 
to fall below the 3.2 mg liter -1 instantaneous minimum. Therefore any future observed 
exceedences of this criterion value are likely due to anthropogenic nutrient pollutant 
loadings, not natural wetland-caused oxygen deficits. 

At attainment levels sustained for long periods of time just above the 4 mg liter -1 
criterion concentration (e.g., very few observed concentrations above 4 mg liter -1 ), 
survival of open-water aquatic species in their larval, juvenile and adult lifestages 
will not be impaired but there is likely to be some unquantified level of growth- 
related impairments. However, the 18-year data record indicates a maximum of less 
than one-third of the segment-based dissolved oxygen concentrations would not 
attain a 5 mg liter -1 concentration (Table VI-4). Therefore, combined with imple¬ 
mentation of further nutrient reduction actions in the upstream watersheds yielding 
higher measured ambient dissolved oxygen concentrations in the future, the number 
of exceedences of the 5 mg liter -1 concentration will be even less, further limiting 
growth effects. 

With a 30-day mean criterion of 4 mg liter -1 , these segments are likely to pass or 
come close to passing a formal criteria assessment under current conditions. Given 
that some fraction of oxygen depletion in these segments is definitely caused by 
controllable nutrient inputs, tributary-based nutrient reduction strategies should be 
more than adequate to raise ambient oxygen levels above the 4 mg liter -1 
concentration. 

SITE-SPECIFIC CRITERIA BIOLOGICAL REFERENCE CURVE 

The criteria assessment protocol for all segments and designated uses employs moni¬ 
toring data to develop cumulative frequency distribution (CFD) curves of 
exceedance, which are compared to biological reference curves specific to desig¬ 
nated uses, salinity regimes, and seasons. Monitoring data are interpolated over a 
fixed three-dimensional grid to obtain dissolved oxygen concentrations for each grid 
cell. These are compared to appropriate criteria values and yield a grid-cell by grid¬ 
cell estimate of the volume or area of criteria exceedance. The percentages of a 
segment’s volume/area exceeding the criteria levels are accumulated over all obser¬ 
vation dates in the assessment period. The CFD generated from these data reflect 
exceedance (and by difference, attainment) in both space and time. (See Chapter 6 
of Ambient Water Quality Criteria for Dissolved Oyxgen, Water Clarity and Chloro¬ 
phyll a for the Chesapeake Bay and Its Tidal Tributaries (U.S. EPA 2003a) for more 
details on the criteria attainment assessment protocol.) The biological reference 
curve is the CFD of exceedances in segments or other areas that are determined to 


chapter Vi 


Guidance for Deriving Site Specific Dissolved Oxygen Criteria 





83 


be ‘healthy,’ i.e., that demonstrably support growth and reproduction of the living 
resources targeted for protection by these criteria. 

The biological reference levels are, by definition, based on ambient dissolved 
oxygen conditions exhibited by areas supporting high functioning living resources. 
Even if this definition were abandoned in favor of a curve or curves based on specific 
natural impairments, then the Mattaponi and Pamunkey segments would have to 
serve as their own reference sites, which is difficult to rationalize. In the absence of 
sufficient data necessary to generate a biological reference curve, EPA recommends 
application of a normal distribution curve representing approximately 10 percent 
allowable criteria exceedence (U.S. EPA 2003a). 


LITERATURE CITED 

Anderson, I. C., C. R. Tobias, B. B. Neikirk and R. L. Wetzel. 1997. Development of a 
process-based mass balance model for a Virginia Spartina alterniflora salt marsh: Implica¬ 
tions for net DIN flux. Marine Ecology Progress Series 159:13-27. 

Cai, W. J., L. R. Pomeroy, M. A. Moran and Y. Wang. 1999. Oxygen and carbon dioxide mass 
balance for the estuarine-intertidal marsh complex of five rivers in the southeastern U.S. 
Limnology' and Oceanography 44:639-649. 

Neubauer, S. C., I. C. Anderson, J. A. Constantine and S. A. Kuehl. 2001. Sediment deposi¬ 
tion and accretion in a mid-Atlantic (U.S.A.) tidal freshwater marsh. Estuarine Coastal and 
Shelf Science. 54:713-727. 

Neubauer, S. C., W. D. Miller and I. C. Anderson. 2000. Atmospheric C0 2 evasion, dissolved 
inorganic carbon production and net heterotrophy in the York River estuary. Limnology and 
Oceanography. 45:1701-1717. 

Neubauer, Scott. June 6, 2003 and June 19, 2003. Personal communication. Smithsonian 
Institute Environmental Research Center, Edgewater, Maryland. 

Tobias, C.R., EC. Anderson, E.A. Canuel, and S.A. Mako. 2001. Nutrient cycling through a 
fringing marsh—aquifer ecotone. Marine Ecology Progress Series. 210:25-39. 

U.S. EPA. 2003a. Ambient Water Quality' for Dissolved Oxygen, Water Clarity / and Chloro¬ 
phyll a for the Chesapeake Bay and Its Tidal Tributaries. EPA 903-R-03-002. Region III 
Chesapeake Bay Program Office, Annapolis, Maryland. 

U.S. EPA. 2003b. Technical Support Documentation for Identification of Chesapeake Bay 
Designated Uses and Attainability'. EPA 903-R-03-004. Region III Chesapeake Bay Program 
Office, Annapolis, Maryland. 


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Guidance for Deriving Site Specific Dissolved Oxygen Criteria 


















85 


chapter VII 

Upper and Lower Pycnocline 
Boundary Delineation 
Methodology 


Vertical stratification is foremost among the physical factors affecting dissolved 
oxygen concentrations in some parts of Chesapeake Bay and its tidal tributaries. If 
the density discontinuity is great enough to prevent mixing of the layers and consti¬ 
tutes a vertical barrier to diffusion of dissolved oxygen, then a pycnocline is said to 
exist (Figure VII-1). For the purposes of water quality criteria attainment assessment, 
the Chesapeake Bay and tidal tributary waters are separated into a surface mixed 
layer (e.g., open-water designated use), an inter-pycnocline layer (e.g., deep-water 
designated use) and a lower mixed layer (e.g., deep-channel designated use) (U.S. 
EPA 2003a, 2003b). 

Accurate estimates of the pycnocline are important for assessing criteria attainment. 
The method documented here for assessing upper and lower mixed layer depths 
differs from the standard Chesapeake Bay Water Quality Monitoring Program field 
sampling cruise method (Chesapeake Bay Program 1996) in that this methodology 
uses a measured density gradient based on salinity and temperature rather than 
relying on the field surrogate, conductivity. 

Defining the depth of the upper mixed layer based on the physical barrier of a density 
gradient is discussed in Brainerd and Gregg 1995. Culver and Perry (1999) and 
Larsson et al. (2001) propose particular density gradient thresholds for defining this 
layer. The critical density gradient is dependent on many factors, most importantly 
the strength of the turbulent mixing. Generally, for the Chesapeake Bay the upper 
pycnocline depth, defining the surface mixed layer, is the shallowest occurrence of a 
density gradient of 0.1 kg/m 4 or greater. The lower mixed layer depth is the deepest 
occurrence of a density gradient of 0.2 kg/m 4 , if a lower mixed layer exists below it. 
These limits were based on an extensive review of thousands of density profiles 
throughout the Chesapeake Bay and its tidal tributaries throughout 19-year record of 
the Chesapeake Bay Water Quality Monitoring Program. These density gradient 
thresholds are consistent with the values published for other tidal water bodies and 
with similar studies in the Chesapeake Bay (Fisher 2003). Since pycnocline delin- 


chapter vii 


Upper and Lower Pycnocline Boundary Delineation Methodology 


86 


eation is based on hydrodynamics and not bathymetry, the depth of the pycnocline 
and hence the boundaries of the designated uses changes on a monthly basis. 


DETERMINATION OF THE VERTICAL DENSITY PROFILE 

The vertical water column density profile (sigma-t) is calculated using the following 
equations: 

Sigma_t = tsum+((sigo+0.1324)*( l-sa+sb*(sigo -0.1324))) 

Where: 

tempc = water temperature in degrees Celsius 
salinity = salinity in grams per liter 

sigo = -0.069+(( 1.47808*((salinity - 0.03)/1.805))(0.00157* 

(((salinityBO.03 )/l.805 )**2))+0.0000398* 

(((salinityB0.03)/l .805)**3))); 

tsum = (-l*(((tempc - 3.98)**2)/503.57))* ((tempc+283)/(tempc+67.26)); 

sa = (10**-3)*tempc)*(4.7867 - (0.098185*tempc)+(0.0010843* 
(tempc**2))), 

and 

sb = ((10**-6)*tempc)*( 18.030-(0.8164*tempc)+(0.01667*(tempc**2))). 


DETERMINATION OF THE PYCNOCLINE DEPTHS 

To determine the depths of the pycnocline, the following rules are applied to the 

density profile: 

1) From the water surface downward, the first density slope observation that is 
greater than 0.1 kgnr 4 is designated as the upper pycnocline depth provided that: 

a) that observation is not the first observation in the water column; and 

b) the next density slope observation below is positive. 

2) From the bottom sediment-water interface upward, the first density slope obser¬ 
vation that is greater than 0.2 kg nr 4 is designated as the lower pycnocline depth 
provided that: 

a) an upper pycnocline depth exists; 

b) there is a bottom mixed layer, defined by the first or second density 
slope observation from the bottom sediment-water interface being less 
than 0.2 kg m' 4 ; and 

c) the next density slope observation above is positive. 


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87 



Figure VIM. Example of a vertical density profile with calculated pycnocline boundaries 
and observed dissolved oxygen concentrations with depth. Monitored water column 
density and observed dissolved oxygen concentrations with depth are illustrated with the 
upper (dashed line) and lower (dotted line) pycnocline depths overlaid for station CB4.3 in 
the middle Chesapeake Bay mainstem on June 10, 1986. 


LITERATURE CITED 

Brainerd, K. E. and M. C. Gregg. 1995. Surfaced mixed and mixing layer depths. Deep-Sea 
Research 42: 1521-1543 

Chesapeake Bay Program. 1996. Recommended Guidelines for Sampling and Analyses in the 
Chesapeake Bay Monitoring Program. EPA 903-R-96-006. CBP/TRS 148/96. Chesapeake 
Bay Program Office, Annapolis, Maryland. 

Culver, M. E. and M. J. Perry. 1999. The response of photosynthetic absorption coefficients 
to irradiance in culture and in tidally mixed estuarine waters. Limnology> and Oceanography 
44: 24-36. 

Fisher, Tom. 2003. Personal communication/unpublished manuscript. University of Mary¬ 
land Center for Environmental Science, Horn Point Laboratory, Cambridge, Maryland. 

Larsson, U., S. Hajdu, J. Waive, and R. Elmgren. 2001. Baltic Sea nitrogen fixation estimated 
from the summer increase in upper mixed layer total nitrogen. Limnology ; and Oceanography 
46: 811-820. 

U.S. Environmental Protection Agency. 2003a. Ambient Water Quality; Criteria for Dissolved 
Oxygen, Water Clarity’ and Chlorophyll a far the Chesapeake Bay and Its Tidal Tributaries. 
EPA 903-R-03-002. Region III Chesapeake Bay Program Office. Annapolis, Maryland. 

U.S. Environmental Protection Agency. 2003b. Technical Support Document for Identifica¬ 
tion of Chesapeake Bay Designated Uses and Attainability. EPA 903-R-03-004. Region III 
Chesapeake Bay Program Office, Annapolis, Maryland. 


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89 


chapter \/BIi 

Updated Guidance for 
Application of Water Clarity 
Criteria and SAV Restoration 

Goal Acreages 


With publication of the Ambient Water Quality Criteria for Dissolved Oxygen, Water 
Clarity and Chlorophyll a for the Chesapeake Bay and Its Tidal Tributaries 
(Regional Criteria Guidance) (U.S. EPA 2003a) and the Technical Support Docu¬ 
ment for Identification of Chesapeake Bay Designated Uses and Attainability- 
(Technical Support Document) (U.S. EPA 2003b), the jurisdictions were provided 
with extensive guidance for how to determine attainment of the shallow-water bay 
grass designated use. 

Specifically, the EPA Regional Criteria Guidance document provided the following 
guidance to the jurisdictions: 

To determine the return of water clarity conditions necessary to support 
restoration of underwater grasses and, therefore, attainment of the shallow- 
water designated use, states may: 1) evaluate the number of acres of 
underwater bay grasses present in each respective Chesapeake Bay Program 
segment, comparing that acreage with the segment’s bay grass restoration 
goal acreage; and/or 2) determine the attainment of the water clarity criteria 
within the area designated for shallow-water bay grass use. The shallow- 
water bay grass use designated use area may be defined by either: 

1) applying the appropriate water clarity criteria application depth (i.e., 0.5, 

1 or 2 meters) along the entire length of the segment's shoreline (with excep¬ 
tion of those shoreline areas determined to be bay grass no-zone grow zones; 
see U.S. EPA 2003 [Technical Support Document ] for details); or 

2) determining the necessary total acreage of shallow-water habitat within 
which the water clarity criteria must be met using a salinity regime specific 
ratio of underwater bay grass acres to be restored within a segment to acres 
of shallow-water habitat that must meet the water clarity criteria within the 
same segment (regardless of specifically where and at what exact depth 
those shallow water habitat acreages reside within the segment). 


chapter vii 


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90 


These approaches to assessing attainment of the shallow-water bay grass designated 
use were described in more detail in Chapter 6 of the Regional Criteria Guidance 
document (U.S. EPA 2003a). Since the 2003 publication of both the Regional 
Criteria Guidance and the Technical Support Document , new information has 
become available to the watershed jurisdictions and EPA in support of state adoption 
of SAV restoration goal, shallow water habitat and shallow-water existing use 
acreages into their water quality standards regulations. This new information will 
also help the four jurisdictions with Chesapeake Bay tidal waters adopt consistent, 
specific procedures for determining attainment of the shallow-water bay grass desig¬ 
nated uses into their regulations. (Note the terms ‘underwater bay grasses’ and 
‘submerged aquatic vegetation’ or ‘SAV’ are used interchangeably in this document.) 

EPA continues to support and encourage the jurisdictions’ adoption of the Chesapeake 
Bay Program segment-specific submerged aquatic vegetation (SAV) restoration goal 
acreages and the corresponding water clarity criteria attaining shallow-water acreage 
necessary to support restoration of those acreages of SAV into each jurisdictions’ 
respective water quality standards regulations. Achievement of the SAV restoration 
goal and shallow-water acreages are two additional means, beyond numerical water 
clarity criteria applied to segment-specific application depths, for defining attainment 
of the shallow-water bay grass designated use. 


WATER CLARITY CRITERIA APPLICATION PERIODS 

The temporal application periods for the water clarity criteria were determined based 
on the growing seasons for the salinity-based SAV plant communities: April 1 
through October 31 for tidal fresh, oligohaline and mesohaline salinity regimes and 
March 1 through May 31 and September 1 through November 30 for polyhaline 
regimes (U.S. EPA 2003a; Batiuk et al. 1992, 2000). The tidal fresh, oligohaline and 
mesohaline salinity regimes application period was based on the combined growing 
seasons for tidal fresh to middle salinity SAV species communities. The polyhaline 
temporal application periods were based on the bimodal Zoster a marina or eelgrass 
growing seasons (Batiuk et al. 1992). 

Given that Ruppia maritima or widgeon grass, principally a mesohaline species, has 
been found growing along with eelgrass in a majority of the polyhaline regions of 
the Chesapeake Bay and its tidal tributaries in Virginia waters (Moore et al. 2000), 
the water clarity criteria temporal application period for polyhaline waters should be 
an inclusive combination of the mesohaline and polyhaline temporal application 
periods or March 1 through November 30. This expanded temporal application 
period should apply to polyhaline Chesapeake Bay Program segments where there is 
evidence of past or present widgeon grass growth or the potential for future growth. 


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91 


SHALLOW-WATER HABITAT ACREAGES 

New information on shallow-water habitat acreages has been published in the Tech¬ 
nical Support Document for Identification of Chesapeake Bay Designated Uses and 
Attainabilit)'-2004 Addendum (U.S. EPA 2004). These updated shallow-water 
habitat acreages factor in the full extent of the 0 to 2 meter depth contour area of 
shallow water habitat, minus the delineated SAV no-grow zones. Through compar¬ 
ison with the expanded restoration acreages, described below, new segment-specific 
expanded restoration acreages as a percentage of the shallow-water habitat acreages 
have also been published in the Technical Support Document 2004 Addendum. 

SAV RESTORATION ACREAGE TO SHALLOW-WATER HABITAT 
ACREAGE RATIO 

There is scientific documentation originally published in both the Ambient Water 
Quality- Criteria for Dissolved Oxygen, Water Clarity and Chlorophyll a for the 
Chesapeake Bay and its Tidal Tributaries (U.S. EPA 2003a) and the Technical 
Support Document for Identification of Chesapeake Bay Designated Uses and 
Attainability (U.S. EPA 2003b) supporting the findings that suitable shallow-water 
habitat must be at acreages greater than the corresponding SAV restoration goal to 
support restoration of SAV to those acreages. 

Text on page 198 in the Regional Criteria Guidance states: 

Restoring underwater water grasses within a segment requires that the 
particular shallow-water habitat meet the Chesapeake Bay water clarity 
criteria across acreages much greater than those actually covered by bay 
grasses. The ratio of underwater bay grass acreage to the required shallow- 
water habitat acreage achieving the necessary level of water clarity to 
support return of those underwater bay grasses varies based upon the 
different species of bay grasses inhabiting the Chesapeake Bay’s four 
salinity regimes. The baywide average ratio of underwater bay grass acreage 
to suitable shallow-water habitat acreage is approximately one acre of 
underwater bay grasses for every three acres of shallow-water habitat 
achieving the Chesapeake Bay water clarity criteria. 

The salinity regime and, therefore, bay grass community-specific under¬ 
water bay grass acreage to shallow-water habitat acreage ratios have been 
derived through an evaluation of extensive underwater bay grass distribution 
data within tidal-fresh, low (oligohaline), medium (mesohaline) and high 
(polyhaline) salinity regimes (reflecting different levels of coverage by 
different bay grass communities). The Technical Support Document for the 
Identification of Chesapeake Bay Designated Uses and Attainability docu¬ 
ments the methodology followed and the resulting bay grasses acreage to 
shallow water habitat acreage ratios derived for each of the four salinity 
regimes (U.S. EPA 2003). 


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92 


Text on page 123 in the Technical Support Document states: 

As described previously, the restoration of underwater bay grasses within a 
segment requires that shallow-water habitat meet the Chesapeake Bay water 
clarity criteria over a greater acreage than the underwater bay grasses will 
actually cover. The ratio of underwater bay grass acreage to the required 
shallow-water habitat acreage varies based on the different species of under¬ 
water bay grasses that inhabit the Bay’s four salinity regimes. Shallow-water 
habitat acreage ratios have been derived scientifically through evaluation of 
extensive underwater bay grasses distribution data within tidal fresh, low, 
medium and high salinity regimes (reflecting different levels of coverage by 
different underwater bay grass communities). 

The Chesapeake Bay Program segment-specific restoration goal acreage and 
corresponding shallow-water designated use acreage (to the previously 
determined maximum depth of abundant and persistent underwater plant 
growth) listed in Table IV-15 were summed by major salinity regimeBtidal 
fresh (0-0.5 ppt), oligohaline (> 0.5-5 ppt), mesohaline (> 5ppt— 18 ppt) and 
polyhaline (>18 ppt). The underwater bay grasses acreage to shallow-water 
habitat acreage ratios were then expressed as a percentage of the total 
shallow-water designated use habitat. Compared with a baywide value of 38 
percent, the tidal-fresh (37 percent), mesohaline (39 percent) and polyhaline 
(41 percent) values were all very close to the baywide value as well as the 
other salinity regime-specific values (Table IV-16). These values are consis¬ 
tent with findings published in the scientific literature and the 35 to 48 
percent range derived from evaluation of the 1930s through early 1970s 
historical data record by Naylor (2002) and Moore (1999, 2001). Influenced 
by the natural presence of the estuarine turbidity maximum, the value was 
21 percent in oligohaline habitats. 

The scientific literature along with analysis of the multi-decadal SAV aerial survey 
data record confirm that healthy SAV beds cover only a portion of the available suit¬ 
able habitat due to a variety of natural reasons. Given that the information 
summarized above and further documented in the Technical Support Document-2004 
Addendum indicates ratios from 1:2 to 1:3 in terms of the area covered by SAV beds 
compared to available shallow-water habitat area, a 1:2.5 ratio is recommended for 
determining the segment-specific acreage of shallow-water habitat that needs to 
achieve the applicable water clarity criteria required to support restoration of the 
segment specific SAV goal acreage. 


SAV RESTORATION GOAL ACREAGES 

The adopted Chesapeake Bay Program SAV restoration goal acreages were based on 
single best year coverages artificially clipped for shoreline and segment-specific 
water clarity criteria application depths, undercounting the actual mapped SAV 
acreages. In some segments, this resulted in the existing use acreages being higher 
than the restoration goal acreage. The chosen solution, described in more detail in 


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93 


the Technical Support Document-2004 Addendum , was to count all of the SAV 
acreage for a given segment that occurred within the single best year regardless of 
any shoreline, bathymetry data limitations or water clarity application depth restric¬ 
tions. 

The Technical Support Document-2004 Addendum documents the ‘expanded 
restoration acreage’, updated existing use acreage and the available shallow-water 
habitat area for each Chesapeake Bay Program segment (U.S. EPA 2004). As 
described in the addendum: 

The ‘expanded restoration acreage’ is the greatest acreage from among the 
updated existing use acreage (1978-2002; no shoreline clipping), the Chesa¬ 
peake Bay Program adopted SAV restoration goal acreage (strictly adhering 
to adopted single best year methodology with clipping) and the goal acreage 
displayed without shoreline or application depth clipping and including SAV 
from areas still lacking bathymetry data. This ‘expanded restoration 
acreage’ is being documented here and provided to the partners as the best 
acreage values that can be directly compared with SAV acreages reported 
through the baywide SAV aerial survey. These acreages are not the officially 
adopted goals of the watershed partners; they are for consideration by the 
jurisdictions when adopting refined and new water quality standards 
regulations. 

The Chesapeake Bay Program SAV restoration goal of 185,000 acres and the 
segment-specific goal acreages stand as the watershed partners’ cooperative restora¬ 
tion goal for this critical living resource community (Chesapeake Executive Council 
2003). EPA recommends that the jurisdictions with Chesapeake Bay tidal waters 
consider adopting the expanded restoration acreages (which factor in the updated 
existing use acreages) and shallow-water habitat acreages determined using the 1:2.5 
ratio into their refined and new water quality standards regulations. 


DETERMINING ATTAINMENT OF THE 
SHALLOW-WATER BAY GRASS USE 

In addition to the methods previously described in the Technical Support Document 
(U.S. EPA 2003b) for determining attainment of the shallow-water bay grass desig¬ 
nated use, there is an additional methodology which integrates both progress towards 
to the SAV restoration goal acreage and measurement of suitable shallow water 
habitat acreage necessary to support restoration of the remaining SAV beds needed 
to reach the goal acreage. This methodology calls for assessing attainment of the 
shallow-water designated use in a segment through a combination of mapped SAV 
acreage and meeting the applicable water clarity criteria in an additional, unvege¬ 
tated shallow water surface area equal to 2.5 times the remaining SAV acreage 
necessary to meet the segment’s restoration goal (SAV restoration goal acreage 
minus the mapped SAV acreage). In other words, a segment’s shallow-water bay 
grass designated use would be considered in attainment if there are sufficient acres 


chapter vii 


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94 


of shallow-water habitat meeting the applicable water clarity criteria to support 
restoration of the remaining acres of SAV, beyond the SAV beds already mapped, 
necessary to reach that segment’s SAV restoration goal acreage. These measure¬ 
ments of SAV acreages and water clarity levels would be drawn from three years of 
data as previously described in the Regional Criteria Guidance (U.S. EPA 2003a). 

Here’s a hypothetical example of determining attainment of the shallow-water bay 
grass use using both mapped SAV acreage and shallow-water habitat acreage 
meeting the water clarity criteria. Segment X has an SAV restoration goal acreage of 
1,400 acres. Over the past three years, SAV beds totaling 1,100 acres have been 
mapped within the segment for at least one of the three years. Therefore, the 
remaining SAV acreage necessary to meet the segment’s restoration goal is 1,400 
acres (SAV restoration goal) minus 1,100 acres (SAV currently mapped) or 300 
acres. Beyond the currently vegetated shallow-water habitat, an additional 750 acres 
of shallow-water habitat (2.5 times 300 acres) would need to attain the water clarity 
criteria in order to determine that this segment is attaining the shallow-water bay 
grass use in combination with the 1,100 acres of mapped SAV. 


LITERATURE CITED 

Batiuk, R. A., P. Bergstrom, M. Kemp. E. Koch, L. Murray, J. C. Stevenson, R. Bartleson, V. 
Carter, N. B. Rybicki, J. M. Landwehr, C. Gallegos, L. Karrh, M. Naylor, D. Wilcox, K. A. 
Moore, S. Ailstock and M. Teichberg. 2000. Chesapeake Bay Submerged Aquatic Vegetation 
Water Quality and Habitat-Based Requirements and Restoration Targets: A Second Technical 
Synthesis. CBP/TRS 245/00 EPA 903-R-00-014. U.S. EPA Chesapeake Bay Program, 
Annapolis, Maryland. 

Batiuk. R. A., R. Orth, K. Moore, J. C. Stevenson. W. Dennison. L. Staver, V. Carter, N. B. 
Rybicki, R. Hickman, S. Kollar and S. Bieber. 1992. Chesapeake Bay Submerged Aquatic 
Vegetation Habitat Requirements and Restoration Targets: A Technical Synthesis. CBP/TRS 
83/92. U.S. EPA Chesapeake Bay Program, Annapolis, Maryland. 

Chesapeake Executive Council. 2003. Chesapeake Executive Council Directive No. 02-03: 
Meeting the Nutrient and Sediment Reduction Goals. Annapolis, Maryland. 

Moore, K„ D. Wilcox, R. Orth and E. Bailey. 1999. Analysis of historical distribution of 
submerged aquatic vegetation (SAV) in the James River. Special Report No. 355 in Applied 
Marine Science and Ocean Engineering. Virginia Institute of Marine Science, School of 
Marine Science, College of William and Mary, Gloucester Point, Virginia. 

Moore, K. A., D.J. Wilcox and R. J. Orth. 2000. Analysis of the abundance of submersed 
aquatic vegetation communities in the Chesapeake Bay. Estuaries 23 (1): 1 15-127. 

Moore, K., D. Wilcox and B. Anderson. 2001. Analysis of historical distribution of 
submerged aquatic vegetation (SAV) in the York and Rappahannock rivers as evidence of 
historical water quality conditions. Special Report No. 375 in Applied Marine Science and 
Ocean Engineering. Virginia Institute of Marine Science, School of Marine Science, College 
of William and Mary, Gloucester Point, Virginia. 


chapter vii 


Updated Guidance for Application of Water Clarity Criteria and SAV Restoration Goal Acreages 






Naylor, M.D. 2002. Historic distribution of submerged aquatic vegetation (SAV) in Chesa¬ 
peake Bay, Maryland. Maryland Department of Natural Resources, Annapolis, Maryland. 

U.S. Environmental Protection Agency. 2003a. Ambient [Voter Quality Criteria for Dissolved 
Oxygen, Water Clarity ; and Chlorophyll a for the Chesapeake Bay and Its Tidal Tributaries. 
EPA 903-R-03-002. Chesapeake Bay Program Office, Annapolis, Maryland. 

U.S. Environmental Protection Agency. 2003b. Technical Support Document for Identifica¬ 
tion of Chesapeake Bay Designated Uses and Attainability. EPA 903-R-03-004. Region III 
Chesapeake Bay Program Office, Annapolis, Maryland. 

U.S. Environmental Protection Agency. 2004. Technical Support Document for Identification 
of Chesapeake Bay Designated Uses and Attainability-2004 Addendum. EPA 903-R-04-006. 
Region 111 Chesapeake Bay Program Office, Annapolis, Maryland. 


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97 


cha pter IX 

Determining Where Numerical 
Chlorophyll a Criteria Should 
Apply to Local Chesapeake Bay 
and Tidal Tributary Waters 


As published in Ambient Water Quality Criteria for Dissolved Oxygen, Water Clarity 
and Chlorophyll a for Chesapeake Bay and Its Tidal Tributaries (U.S. EPA 2003): 

The EPA expects states to adopt narrative chlorophyll a criteria into their 
water quality standards for all Chesapeake Bay and tidal tributary waters. 

The EPA strongly encourages states to develop and adopt site-specific 
numerical chlorophyll a criteria for tidal waters where algal-related impair¬ 
ments are expected to persist even after the Chesapeake Bay dissolved 
oxygen and water clarity criteria have been attained. 

The Chesapeake Bay Program partners developed a general methodology for 
possible use by the jurisdictions with tidal waters to determine consistently which 
local tidal waters will likely attain the published Chesapeake Bay dissolved oxygen 
and water clarity criteria yet algal-related water quality impairments will persist. The 
methodology is for application by Maryland, Virginia, Delaware and the District of 
Columbia to assist in their future determinations of where they need to derive and 
apply numerical chlorophyll a criteria for localized tidal waters. 


RECOMMENDED METHODOLOGY 

The jurisdictions should evaluate the available Chesapeake Bay Water Quality Moni¬ 
toring Program’s time series of spring and summer chlorophyll a concentrations on 
a station by station, segment by segment basis and compare these concentrations to 
a range of season and salinity regime-based target chlorophyll a concentrations. 
Target concentrations, examples given in Table IX-1, should be derived from 
published chlorophyll a concentrations associated with an array of water quality and 
biological community effects and impairments. The jurisdictions should then iden¬ 
tify those stations/segments that are persistently higher than the applicable target 
chlorophyll a concentrations with the individual jurisdictions developing their own 


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98 


Table IX-1 . Example numerical chlorophyll a thresholds (p g liter 1 ) drawn from Ambient Water Quality Criteria 
for Dissolved Oxygen, Water Clarity and Chlorophyll a for Chesapeake Bay and its Tidal Tributaries' 
reflective of an array of historical concentrations, ecosystem trophic status, potential harmful algal 
blooms, water quality impairments, user perceptions and state water quality standards. 



Chlorophyll a Concentration Thresholds (pg liter' 1 ) 

Salinity 

Regime 

Historical 

Chesapeake 

Bay Levels 2J 

Ecosystem 
Trophic Status 

Phytoplankton 

Reference 

Communities 6 

Potentially 
Harmful Algal 
Blooms 7 

Water Quality 
Impairments 8 

User 

Perceptions 

State Water 

Quality 

Standards" 

Tidal Fresh 

Spring: 4 

Summer: 7 

Mainstem 
(annual): 3 

2-15 4 

Spring: 4.3 
Summer: 8.6 

Microcystis 
aeruginosa: 15 

Water Clarity: 

9-16 

Dissolved 

Oxygen: 

4-5 ~ 

Vermont Lakes: 

<15 9 

Minnesota 

Lakes: < 15 1 " 

AL: 16-27 (res.) 
CN: 2-15 (meso.) 
GA: 5-20 (lakes) 
NC: 15(lakes, 
res.) 

Oligohaline 

Spring: 6 

Summer: 8 

Mainstem 
(annual): 3 


Spring: 9.6 
Summer: 6.0 

Microcystis 
aeruginosa: 15 

Water Clarity 

9-16 

Dissolved 

Oxygen: 

7-12 


NC: 40 (tidal) 

Mesohaline 

Spring: 6 

Summer: 8 

Mainstem 
(annual): 4 


Spring: 5.6 
Summer: 7.1 

Prorocentrum 
minimum: 5 

Water Clarity: 

<8 

Dissolved 

Oxygen: 

5-6 


NC: 40 (tidal) 

Polyhaline 

Spring: 4 

Summer: 4 

Mainstem 
(annual): 1 

2-7 5 

Spring: 2.9 
Summer: 4.4 

Prorocentrum 
minimum: 5 

Water Clarity: 

<8 

Dissolved 

Oxygen: 

4-5 


NC: 40 (tidal) 

HW: 2; 5 <10%; 

10 <2% 


Sources: 1. U.S. EPA 2003; 2. Olson 2002; 3. Harding and Perry 1997; 4. Wetzel 2001, Ryding and Rast 1989, Smith et al. 1998, 
Novotny and Olem 1994; 5. Smith. 1998, Molvaer 1997; 6. U.S. EPA 2003; 7. U.S. EPA 2003; 8. U.S. EPA 2003; 9. Smeltzer and 
Heiskary 1990; 10.Heiskary and Walker 1988; 11. U.S. EPA 2003. 


decision rules for defining “persistently higher”. The jurisdictions should finally 
evaluate the degree of non-attainment of the dissolved oxygen and/or water clarity 
criteria within surrounding or “downstream” tidal waters. If these waters are in 
attainment of the dissolved oxygen and water clarity criteria, yet are persistently 
higher than the applicable target chlorophyll a concentrations, then these waters 
should be targeted for adoption of numerical chlorophyll a criteria. 

The jurisdictions should also evaluate results from Chesapeake Bay water quality 
model-simulated water quality conditions with achievement of the assigned 
nitrogen, phosphorus and sediment cap load allocations. The jurisdictions would 
then identify those Chesapeake Bay Program segments where the model simulated 
surface chlorophyll a concentrations are above a range of season and salinity regime- 
based target concentrations. The jurisdictions are encouraged to factor in findings 
from state-generated local TMDL modeling in the smaller tidal tributaries and 
embayments (e.g., Nanticoke River in Delaware, Anacostia River in the District of 
Columbia and several tidal tributaries in Maryland) as an additional source of 


chapter ix 


Determining Where Numerical Chlorophyll a Criteria Should Apply 

















99 


information on anticipated chlorophyll a concentrations upon attainment of the 
dissolved oxygen and/or water clarity criteria. Given that these model-simulated 
results reflect tidal water quality conditions estimated to attain the dissolved oxygen 
criteria 4 , these segments should be targeted for adoption of numerical chlorophyll a. 
The jurisdictions should note that management-applicable Chesapeake Bay water 
quality model results are not available for all 78 Chesapeake Bay Program segments 
(Linker et al. 2002). 


LITERATURE CITED 

Harding, L. W. Jr. and E. S. Perry. 1997. Long-term increase of phytoplankton biomass in 
Chesapeake Bay, 1950-1994. Marine Ecology> Progress Series 157:3952. 

Heiskary, S. A. and W. W. Walker. 1988. Developing phosphorus criteria for Minnesota lakes. 
Lake and Reservoir Management 4:1-10. 

Linker, L.C., G. W. Shenk, P. Wang, C. F. Cerco, A. J. Butt, P. J. Tango and R. W. Savidge. 
2002. A Comparison of Chesapeake Bay Estuary Model Calibration With 1985-1994 
Observed Data and Method of Application to Water Quality’ Criteria. Modeling Subcom¬ 
mittee, Chesapeake Bay Program Office, Annapolis, Maryland. 

Molvaer, J., J. Knutzen, J. Magnusson, B. Rygg, J. Skei and J. Sorensen. 1997. Environ¬ 
mental quality classification in fjords and coastal areas. Statens Forurensningstilsyn 
TA1467, Norway. 36 pp. 

Novotny V. and Olem H. 1994. Water Quality’: Prevention. Identification and Management of 
Diffuse Pollution. Van Nostrand Reinhold. New York, New York. 1054pp. 

Olson, M. 2002. Benchmarks for nitrogen, phosphorus, chlorophyll and suspended solids in 
Chesapeake Bay. Chesapeake Bay Program Technical Report Series, Chesapeake Bay 
Program, Annapolis, Maryland. 

Ryding, S. O. and W. Rast. 1989. The control of eutrophication of lakes and reservoirs. Man 
and the Biosphere Series, Volume /, UNESCO, Parthenon Publication Group, Park Ridge, 
New Jersey. 314 pp. 

Smeltzer, E. and S. A. Heiskary. 1990. Analysis and Applications of Lake User Surv ey Data. 
Lake and Reservoir Management 6( 1): 109-118. 

Smith, V. H. 1998. Cultural eutrophication of inland, estuarine and coastal waters. In: Pace, 
M. L. and P. M. Groffman (eds.). Successes, Limitation and Frontiers in Ecosystem Science. 
Springer-Verlag, New York, New York. Pp. 7-49. 

U.S. Environmental Protection Agency. 2003. Ambient Water Quality’ Criteria for Dissolved 
O.xvgen, Water Clarity’ and Chlorophyll a for the Chesapeake Bay and Its Tidal Tributaries. 
EPA 903-R-03-002. Region III Chesapeake Bay Program Office, Annapolis, Maryland. 

Wetzel, R. G. 2001. Limnology’—Lake and River Ecosystems, 3 rd Edition. Academic Press, 
New York, New York. 


4 The applicable water clarity may not be attained within the model simulated output given suspended 
sediment contributions to reduced water clarity conditions independent of the algal contribution to 
reduced water clarity conditions. 


chapter ix 


Determining Where Numerical Chlorophyll a Criteria Should Apply 




s 






















































appendix 


Wetland Area, Segment 
Perimeter/Area/Volume 
and Water Quality 
Parameter Statistics for 
Chesapeake Bay 
Tidal Fresh and 
Oligohaline Segments 



102 


Table A-1. Wetland area, perimeter, surface area and volume statistics for Chesapeake Bay tidal fresh and 
oligohaline segments. 


Chesapeake Bay Program Segment 

Wetland 

Acreage 

(acres) 

Segment 

Perimeter 

(meters) 

Segment 
Surface Area 
(meters 2 ) 

Segment 

Volume 

(meters 1 ) 

Surface Area 
to Volume 
Ratio 

Western Branch Patuxent River-tidal fresh region 

WBRTF 

5181 

131511 



Appomattox River-tidal fresh region 

APPTF 

168938 

8011611 

1510000 

5.3 

Piscataway Creek-tidal fresh region 

PISTF 

15219 

3708997 

2850000 

1.3 

Chester River-tidal fresh region 

CHSTF 

60350 

4084016 

3362500 

1.2 

Pocomoke River-tidal fresh region 

POCTF 

77456 

3998871 

4470000 

0.9 

Nanticoke River-tidal fresh region 

NANTF 

69276 

4608463 

6615000 

0.7 

Mattawoman Creek-tidal fresh region 

MATTF 

37045 

7280895 

9500000 

0.8 

* Patuxent River-tidal fresh region 

PAXTF 

55373 

4408622 

11025000 

0.4 

*Choptank River-tidal fresh region 

CHOTF 

153218 

9466475 

15322500 

0.6 

Bohemia River-oligohaline region 

BOHOH 

79964 

11927636 

17000000 

0.7 

Pocomoke River-oligohaline region 

POCOH 

116755 

13821501 

18000000 

0.8 

Back River-oligohaline region 

BACOH 

64832 

16175354 

22375000 

0.7 

C&D Canal-oligohaline region 

C&DOH 

35654 

3565828 

24130000 

0.1 

Middle River-oligohaline region 

MIDOH 

93914 

16214070 

25000000 

0.6 

Northeast River-tidal fresh region 

NORTF 

40617 

15817689 

26500000 

0.6 

*Patuxent River-oligohaline region 

PAXOH 

76397 

14243456 

27180000 

0.5 

Chester River-oligohaline region 

CHSOH 

124641 

14790537 

28875000 

0.5 

Nanticoke River-oligohaline region 

NANOH 

238038 

16455330 

45000000 

0.4 

*Choptank River-oligohaline region 

CHOOH 

142681 

14477365 

45125000 

0.3 

Chickahominy River-oligohaline region 

CHKOH 

355816 

27969270 

48562500 

0.6 

Bush River-oligohaline region 

BSHOH 

107046 

30542696 

49250000 

0.6 

* Rappahannock River-oligohaline region 

RPPOH 

112097 

19536530 

53580000 

0.4 

Gunpowder River-oligohaline region 

GUNOH 

163323 

41998392 

64250000 

0.7 

Sassafras River-oligohaline region 

SASOH 

161366 

33085712 

84187500 

0.4 

Elk River-oligohaline region 

EFKOH 

138710 

37270004 

101250000 

0.4 

* Rappahannock River-tidal fresh region 

RPPTF 

252716 

36503308 

107437500 

0.3 

James River-tidal fresh region 

JMSTF 

562776 

95301848 

286187500 

0.3 

Chesapeake Bay-tidal fresh region 

CB1TF 

216814 

151620944 

360000000 

0.4 

James River-oligohaline region 

JMSOH 

271459 

127749032 

431500000 

0.3 

* Potomac River-tidal fresh region 

POTTF 

365926 

153841616 

484750000 

0.3 

*Potomac River-oligohaline region 

POTOH 

312495 

214963696 

852250000 

0.3 

Chesapeake Bay-oligohaline region 

CB20H 

246410 

275239520 

1237000000 

0.2 


*Segments with similar characteristics or geographically close to the Mattaponi and Pamunkey segments. 
Source: Chesapeake Bay Program http://chesapeakebay.net/data 


appendix a 









103 


Table A-2. Summer average conditions in other tidal fresh and oligohaline Chesapeake Bay Program segments, 
2000 - 2002 . 


Total 


CBP 

Segment 

Water 

Column 

Layer 

Water 

Column 

Depth 

(meters) 

Salinity 

(ppt ) 1 

Temperature 

(°C) 

Dissolved Dissolved 

Oxygen Oxygen 

Concentration Deficit 
(mg liter' 1 ) (mg liter' 1 ) 

Chlorophyll a 
Concentration 
(pg liter') 

Suspended Total 

Solids Nitrogen 

Concentration Concentration 
(mg liter') (mg liter') 

Total 

Phosphorus 
Concentration 
(mg liter') 

APPTF 

S 

0.7 

0.09 

27.90 

8.45 

-0.50 

44.5 

35.5 

1.0771 

0.1169 

APPTF 

B 

5.7 

0.09 

27.44 

7.68 

0.31 


67.7 

1.1839 

0.1656 

CB1TF 

S 

0.5 

0.68 

25.92 

7.32 

0.79 

8.4 

8.0 

1.1310 

0.0389 

CB1TF 

B 

4.8 

0.86 

25.58 

6.79 

1.36 

6.7 

10.1 

1.1603 

0.0387 

JMSTF 

S 

0.7 

0.30 

27.56 

7.82 

0.13 

22.4 

15.9 

0.9022 

0.0989 

JMSTF 

B 

8.8 

0.37 

27.24 

6.94 

1.04 


75.1 

1.1113 

0.1388 

MATTF 

S 

0.3 

0.19 

24.46 

6.98 

1.38 

18.1 

8.1 

0.9551 

0.0608 

NANTF 

S 

0.5 

0.63 

25.86 

5.68 

2.45 

15.6 

23.1 

2.3553 

0.0667 

NANTF 

B 

4.1 

0.67 

25.77 

5.44 

2.69 

14.6 

50.4 

2.3513 

0.0891 

NORTF 

S 

0.5 

0.24 

25.93 

8.70 

-0.57 

44.3 

22.0 

1.1431 

0.0847 

NORTF 

B 

1.8 

0.24 

25.66 

7.91 

0.26 

42.2 

25.7 

1.1207 

0.0876 

PAXTF 

S 

0.2 

0.22 

24.27 

7.37 

1.02 

36.2 

34.4 

1.3724 

0.1547 

PAXTF 

B 

9.4 

0.68 

25.18 

7.28 

0.96 

66.3 

99.9 

1.3846 

0.2731 

PISTF 

S 

0.2 

0.00 

24.22 

6.97 

1.45 

14.2 

10.3 

1.3197 

0.0962 

POCTF 

S 

0.5 

0.61 

26.13 

4.63 

3.46 

7.6 

12.4 

1.6927 

0.1206 

POCTF 

B 

4.9 

0.72 

26.00 

4.64 

3.46 

7.8 

25.8 

1.6005 

0.1408 

POTTF 

S 

0.5 

0.16 

26.54 

7.60 

0.45 

20.4 

13.0 

1.5054 

0.0769 

POTTF 

B 

10.9 

0.24 

25.97 

6.36 

1.76 

18.7 

35.1 

1.6021 

0.1047 

RPPTF 

S 

0.7 

0.71 

26.89 

7.20 

0.84 

31.0 

23.4 

0.9105 

0.0776 

RPPTF 

B 

5.1 

0.75 

26.68 

6.84 

1.10 

. 

37.1 

0.9543 

0.0883 

WBRTF 

S 

0.0 

0.01 

21.97 

6.82 

1.94 

12.8 

37.1 

1.1804 

0.1868 

BACOH 

S 

0.5 

2.82 

25.18 

7.92 

0.24 

81.9 

24.9 

2.4796 

0.2564 

BACOH 

B 

0.8 

2.92 

25.17 

7.26 

0.89 

66.9 

23.9 

2.1900 

0.2347 

BOHOH 

S 

0.5 

1.27 

26.68 

7.73 

0.26 

24.7 

21.6 

0.8554 

0.0653 

BOHOH 

B 

1.8 

1.30 

26.43 

7.27 

0.75 

21.2 

22.6 

0.9143 

0.0666 

BSHOH 

S 

0.5 

1.16 

25.82 

8.19 

-0.05 

28.7 

24.0 

0.9170 

0.0699 

BSHOH 

B 

1.2 

1.17 

25.61 

7.64 

0.53 

28.7 

25.8 

0.9117 

0.0696 

C&DOH 

S 

0.5 

2.03 

25.74 

6.68 

1.41 

10.5 

17.8 

1.2866 

0.0715 

C&DOH 

B 

12.3 

2.08 

25.53 

6.54 

1.57 

3.4 

30.7 

1.2121 

0.0808 

CB20H 

S 

0.5 

5.11 

24.72 

6.68 

1.41 

6.5 

9.9 

0.9548 

0.0526 

CB20H 

B 

11.7 

8.14 

24.21 

4.47 

3.57 

5.5 

24.6 

0.8730 

0.0675 

CHKOH 

S 

0.7 

2.05 

26.41 

6.33 

1.68 

19.1 

24.7 

0.6205 

0.0873 

CHKOH 

B 

3.9 

2.10 

26.21 

6.24 

1.78 

. 

62.5 

0.7355 

0.1338 

CHOOH 

S 

0.5 

1.09 

26.28 

5.66 

2.40 

18.3 

28.2 

1.6772 

0.1042 

CHOOH 

B 

7.5 

1.19 

25.93 

5.36 

2.74 

17.1 

47.5 

1.8115 

0.1311 

CHSOH 

S 

0.5 

0.69 

26.47 

8.13 

-0.09 

61.2 

53.2 

2.2028 

0.1619 

CHSOH 

B 

4.0 

0.71 

26.18 

7.86 

0.23 

59.6 

65.9 

2.1452 

0.1747 

ELKOH 

S 

0.5 

1.68 

25.89 

6.80 

1.27 

4.1 

11.7 

1.1244 

0.0584 

ELKOH 

B 

11.4 

1.77 

25.62 

6.59 

1.52 

3.5 

25.7 

1.1267 

0.0736 

GUNOH 

S 

0.5 

2.23 

25.12 

7.13 

1.06 

10.3 

16.3 

0.6558 

0.0476 

GUNOH 

B 

0.9 

2.24 

25.08 

6.55 

1.64 

10.5 

18.8 

0.6600 

0.0489 

JMSOH 

S 

0.7 

6.20 

26.71 

6.77 

1.03 

8.9 

22.8 

0.5089 

0.0828 

JMSOH 

B 

10.1 

7.00 

26.69 

6.49 

1.28 

. 

73.5 

0.6217 

0.1202 

MIDOH 

S 

0.5 

3.67 

25.42 

7.63 

0.45 

19.3 

10.1 

0.6698 

0.0493 

MIDOH 

B 

2.7 

4.14 

25.07 

5.90 

2.20 

15.7 

13.7 

0.6727 

0.0478 

PAXOH 

S 

0.5 

3.33 

26.36 

5.87 

2.10 

17.3 

28.6 

0.8689 

0.1378 

PAXOH 

B 

3.6 

3.61 

26.08 

5.38 

2.61 

18.0 

56.1 

0.9835 

0.1912 

POTOH 

S 

0.5 

3.00 

25.80 

6.59 

1.44 

8.2 

12.1 

1.1141 

0.0896 

POTOH 

B 

7.8 

3.77 

25.66 

5.92 

2.09 

3.8 

50.9 

1.1603 

0.1258 

RPPOH 

S 

0.7 

3.12 

26.84 

7.40 

0.55 

19.5 

21.9 

0.6160 

0.0753 

RPPOH 

B 

7.2 

3.63 

26.51 

6.40 

1.57 

. 

73.3 

0.8002 

0.1198 

SASOH 

S 

0.5 

0.46 

26.98 

8.30 

-0.32 

71.6 

23.2 

1.6423 

0.1170 

SASOH 

B 

5.2 

0.53 

26.49 

6.62 

1.43 

66.3 

31.9 

1.5082 

0.1254 


Source: Chesapeake Bay Program http://chesapeakebay.net/data 


appendix a 













































LIBRARY OF CONGRESS 



0 016 080 847 0 



U.S. Environmental Protection Agency 
Region III 

Chesapeake Bay Program Office 
Annapolis, Maryland 
1-800-YOUR-BAY 

and 

Region III 

Water Protection Division 
Philadelphia, Pennsylvania 

in coordination with 

Office of Water 

Office of Science and Technology 
Washington, D.C. 























































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